Composite particles, method for producing composite particles, and use thereof

ABSTRACT

In a method for producing composite particles containing polymer particles and silica particles that adhere to the polymer particles, the composite particles are obtained by subjecting a polymerizable monomer to aqueous suspension polymerization in a presence of silica particles and a cellulose compound adsorbing onto the silica particles. The composite particles contain the polymer particles, the silica particles that adhere to surfaces of the polymer particles, and the water-soluble cellulose compound.

TECHNICAL FIELD

The present invention relates to composite particles containing polymerparticles and silica particles that adhere to surfaces of the polymerparticles, a method for producing the composite particles and the usethereof (i.e., an external preparation, a coating agent, an opticalfilm, a resin composition and a molded product).

BACKGROUND ART

Polymer particles having the average particle diameter of 0.01 to 100 μmare used, for example, for an additive (e.g., flatting agent) for acoating agent such as coating material, an additive (e.g., flattingagent) for ink, a main component of or an additive for an adhesive, anadditive (e.g., shrinkage reducing agent) for cultured marble, a papertreating agent, a filler (filler for improving lubricity) for anexternal preparation such as cosmetics, a column packing material forchromatography, a toner additive for developing an electrostatic image,an anti-blocking agent for a film, and a light diffusing agent for alight diffuser (e.g., light diffusion film).

The above polymer particles are generally produced by suspensionpolymerization of a polymerizable monomer. A suspension stabilizer suchas silica is used for the suspension polymerization so that dropletscontaining the polymerizable monomer can be polymerized in a system inwhich the droplets are stably suspended without coalescing. Thus, it ispossible to obtain fine polymer particles having uniform particlediameter distribution.

For example, Patent Literature 1 recites a method including the stepsof; stirring a composition containing an aqueous medium, a polymerizablemonomer, a polymerization initiator, an inorganic dispersant (e.g.,colloidal silica) and an emulsifier so as to form a dispersion in whichoil droplets are dispersed in the aqueous medium; and heating whilestirring the dispersion so as to polymerize the polymerizable monomer.By this method, it is possible to obtain resin particles (polymerparticles) having uniform particle diameter.

CITATION LIST Patent Literature

[Patent Literature 1] WO 2011/062173 A1

SUMMARY OF INVENTION Technical Problem

Recently, compounding polymer particles with silica particles has beenconsidered as one method for allowing the polymer particles to have newproperties or to improve their properties. For example, it isconceivable that hydrophilicity of the surface of the particles andhardness of the particles themselves can be improved by adhering thesilica particles to the surfaces of the polymer particles. Since theparticles whose surface has hydrophilicity are easily dispersed in anaqueous medium, they can be suitably used as an additive (e.g., flattingagent) for an aqueous coating agent such as aqueous coating material andthe like, and as a raw material for an aqueous external preparation suchas lotion. Also, since the hardness of the particles themselves isimproved, improvement in scratch resistance can be expected when theyare used as the additive for a coating agent such as coating material.

By the method disclosed in Patent Literature 1, it is possible to obtainthe resin particle whose surface is covered by an inorganic dispersantin an amount of 0.0001 to 0.02 g/m². However, this method was made forthe purpose of obtaining the resin particle (polymer particle) whosesurface has a small amount of adhered inorganic dispersant such assilica. Accordingly, by this method, adhesion of the inorganicdispersant to the surface of the resin particle is suppressed. Suchsmall amount of silica particles does not strongly adhere to the surfaceof the resin particle obtained by the above method, and easily fall offthe resin particle.

The present invention was made in consideration of the abovecircumstances, an object of which is to provide: a method for producingcomposite particles in which silica particles hardly fall off surfacesof polymer particles; composite particles obtainable by the method; anduse of the composite particles.

Solution to Problem

In a method for producing composite particles of the present invention,the produced composite particles contain polymer particles and silicaparticles that adhere to the polymer particles. The method includes apolymerization step of subjecting a polymerizable monomer to aqueoussuspension polymerization in the presence of silica particles and awater-soluble cellulose compound adsorbing onto surfaces of the silicaparticles, so that the composite particles are obtained.

In the above method for producing the composite particles, thepolymerizable monomer is subjected to the aqueous suspensionpolymerization in the presence of the silica particles and thewater-soluble cellulose compound adsorbing onto the surfaces of thesilica particles, which allows the silica particles to strongly adhereto the surfaces of the polymer particles due to the function of thewater-soluble cellulose compound adsorbing onto the surfaces of thesilica particles. For this reason, it is possible to obtain thecomposite particles in which the silica particles hardly fall off thesurface of the polymer particles.

The composite particles of the present invention contain the polymerparticles, the silica particles that adhere to the surfaces of thepolymer particles, and the water-soluble cellulose compound.

In the composite particles, the silica particles strongly adhere to thesurfaces of the polymer particles because of the water-soluble cellulosecompound being contained, thus, the silica particles hardly fall off thesurfaces of the polymer particles.

An external preparation of the present invention contains the compositeparticles of the present invention.

The external preparation of the present invention has good lubricitybecause it contains the composite particles of the present invention.Also, when the external preparation of the present invention contains anaqueous solvent, it is possible to obtain a good dispersibility of thecomposite particles due to hydrophilicity of the silica particles thatadhere to the surfaces of the polymer particles.

A coating agent of the present invention contains the compositeparticles of the present invention.

Since the coating agent of the present invention contains the compositeparticles of the present invention, it is possible to give the lightdiffusibility to a coating film formed by the coating agent. Also, inthe coating agent of the present invention, the hardness of thecomposite particles is ensured by the silica particles that adhere tothe surfaces of the polymer particles. Thus, the improvement in thescratch resistance of the coating film formed by the coating agent canbe expected. Furthermore, when the coating agent of the presentinvention contains the aqueous solvent, it is possible to obtain anexcellent dispersibility of the composite particles due to thehydrophilicity of the silica particles that adhere to the surfaces ofthe polymer particles.

An optical film of the present invention is obtainable by applying thecoating agent onto a base material.

The optical film of the present invention contains the coating agent ofthe present invention, thus has the light diffusibility.

A resin composition of the present invention contains the compositeparticles of the present invention and a base resin.

The resin composition of the present invention contains the compositeparticles of the present invention, thus has the light diffusibility.

A molded product of the present invention is obtainable by molding theresin composition of the present invention.

Since the molded product of the present invention is obtainable bymolding the resin composition containing the composite particles of thepresent invention, the molded product of the present invention has thelight diffusibility due to containing of the composite particles of thepresent invention.

Advantageous Effects of Invention

The present invention can provide: the method for producing thecomposite particles in which the silica particles hardly fall off thesurfaces of the polymer particles; the composite particles obtainable bythe above method; and the use of the composite particles.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a transmission electron microscope (TEM) image showing anenlarged part of a cross section of a composite particle obtained inExample 1 of the present invention.

FIG. 2 is a transmission electron microscope (TEM) image showing afurther enlarged part of the cross section of the composite particleobtained in Example 1 of the present invention which part is aninterface part between polymer particles and silica particles of thecomposite particle.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the present invention will be described in detail.

[Method for Manufacturing Composite Particles]

The present invention provides a method for producing compositeparticles containing polymer particles and silica particles that adhereto the polymer particles. The method includes a polymerization step ofobtaining the composite particles by subjecting a polymerizable monomerto aqueous suspension polymerization in the presence of silica particlesand a water-soluble cellulose compound adsorbing onto surfaces of thesilica particles.

(Polymerizable Monomer)

The polymerizable monomer used for the producing method of the presentinvention is not particularly limited. However, it is preferable to use,for example, a compound not having a phosphate ester bond but having apolymerizable carbon-carbon double bond (a vinyl bond in a wide sense),hereinafter simply referred to as a polymerizable vinyl monomer.

The polymerizable vinyl monomer is not particularly limited. Examplesthereof include a monofunctional monomer having an alkenyl group (avinyl group in a wide sense) and a polyfunctional monomer having atleast two alkenyl groups (vinyl groups in a wide sense).

Examples of the monofunctional monomer include: α-methylene aliphaticmonocarboxylic acid ester; styrene; styrene derivatives such aso-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene,2,4-dimethylstyrene, p-n-butylstyrene, p-tert-butylstyrene,p-n-hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene,p-n-dodecylstyrene, p-methoxystyrene, p-phenylstyrene, p-chlorostyreneand 3,4-dichlorostyrene; vinyl carboxylates such as vinyl acetate, vinylpropionate and vinyl butylate; acrylic acid derivatives other thanacrylic acid ester, i.e., acrylonitrile, acrylamide and the like; andmethacrylic acid derivatives other than methacrylic acid ester, i.e.,methacrylonitrile, methacrylamide and the like.

Examples of the α-methylene aliphatic monocarboxylic acid ester include:acrylic acid esters such as methyl acrylate, ethyl acrylate, propylacrylate, n-butyl acrylate, isobutyl acrylate, n-octyl acrylate, dodecylacrylate, 2-ethyhexyl acrylate, stearyl acrylate, lauryl acrylate,2-chloroethyl acrylate, phenyl acrylate, 2-(dimethylamino)ethylacrylate, 2-(diethylamino)ethyl acrylate, 2-hydroxyethyl acrylate, and2-hydroxypropyl acrylate; methacrylic acid esters such as methylmethacrylate, ethyl methacrylate, propyl methacrylate, n-butylmethacrylate, isobutyl methacrylate, n-octyl methacrylate, dodecylmethacrylate, 2-ethyhexyl methacrylate, stearyl methacrylate, laurylmethacrylate, phenyl methacrylate, 2-(dimethylamino)ethyl methacrylate,2-(diethylamino)ethyl methacrylate, 2-hydroxyethyl methacrylate, and2-hydroxypropyl methacrylate; and α-haloacrylic acid ester such asmethyl α-chloroacrylate.

Depending on the circumstances, it is possible to use α,β-unsaturatedcarboxylic acids such as acrylic acid, methacrylic acid, maleic acid andfumaric acid as the monofunctional monomer. Any combination of at leasttwo thereof may also be used. Furthermore, as the monofunctionalmonomer, it is possible to use any one or any combination of at leasttwo out of the following, provided that it does not prevent the effectsof the present invention: vinyl ethers such as methyl vinyl ether, ethylvinyl ether, and isobutyl vinyl ether; vinyl ketones such as methylvinyl ketone, hexyl vinyl ketone, and methyl isopropenyl ketone; N-vinylcompounds such as N-vinylpyrrole, N-vinylcarbazole, N-vinylindole, andN-vinylpyrrolidone; and vinylnaphthalene salts.

In the present invention, it is possible to use any one or anycombination of at least two out of the above examples of themonofunctional monomer. Also, among the above examples of themonofunctional monomer, styrene, methyl methacrylate and the like arepreferable as the monofunctional monomer used in the present inventionbecause they are inexpensive.

Examples of the polyfunctional monomer include: divinylbenzene;bifunctional alkylene glycol di(meth)acrylate such as ethylene glycoldi(meth)acrylate, polyethylene glycol di(meth)acrylate (having 2-10repeating units), propylene glycol di(meth)acrylate, polypropyleneglycol di(meth)acrylate (having 2-10 repeating units), 1,3-butyleneglycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, alkoxylatedneopentyl glycol di(meth)acrylate, propoxylated neopentyl glycoldi(meth)acrylate, neopentyl glycol hydroxypivalate di(meth)acrylate, anddioxane glycol di(meth)acrylate; bifunctional alkylenedioldi(meth)acrylate such as butylenediol di(meth)acrylate, hexanedioldi(meth)acrylate, alkoxylated hexanediol di(meth)acrylate,cyclohexanediol di(meth)acrylate, dodecanediol di(meth)acrylate, andtricyclodecanediol di(meth)acrylate; bifunctional ethoxylated bisphenolA di(meth)acrylate such as ethoxylated (having 2-10 repeating units)bisphenol A di(meth)acrylate; trifunctional trimethylolpropanetri(meth)acrylates such as trimethylolpropane tri(meth)acrylate,ethoxylated trimethylolpropane tri(meth)acrylate, pentaerythritoltri(meth)acrylate, and triacryloyloxyethyl phosphate; tetrafunctionaltetra(meth)acrylate such as pentaerythritol tetra(meth)acrylate, andditrimethylolprop ane tetra(meth)acrylate; hexafunctionaldipentaerythritol hexa(meth)acrylate such as dipentaerythritolhexa(meth)acrylate; octafunctional pentaerythritol (meth)acrylate suchas poly(pentaerythritol) acrylate; and nitrogen atom-containingtrifunctional cyclic(meth)acrylate such as ethoxylated isocyanuric acidtri(meth)acrylate. Note that in these application documents, the term“(meth)acrylate” means methacrylate or acrylate.

When the polymerizable vinyl monomer is used as the polymerizablemonomer in the producing method of the present invention, it ispreferable that the polymerizable vinyl monomer contain both amonofunctional monomer and a polyfunctional monomer. In this way, it ispossible to form good cross-linked structures in the polymer particlesand to give an excellent solvent resistance to the composite particles.The amount of the polyfunctional monomer to be used is preferably withinthe range from 0.5 to 50 wt % based on the total amount of thepolymerizable vinyl monomer to be used, and further preferably, withinthe range from 1 to 40 wt %. Thus, it is possible to form more excellentcross-linked structures in the polymer particles and to give moreexcellent solvent resistance to the composite particles.

In the producing method of the present invention, the polymerizablevinyl monomer may be used solely as the polymerizable monomer. It isalso possible to use, in accordance with the kind of the water-solublecellulose compound described later, the polymerizable vinyl monomertogether with any of the polymerizable phosphoric acid monomerrepresented by formulae (1) to (5) described herein below. By using suchcombinations of the polymerizable vinyl monomer and the polymerizablephosphoric acid monomer in accordance with the kind of the water-solublecellulose compound described later, it is possible to improve stabilityof the droplets of the polymerizable monomer in an aqueous medium whenthe polymerizable monomer is subjected to the aqueous suspensionpolymerization. Thus, in the producing method of the present invention,the polymerizable phosphoric acid monomer can be suitably used togetherwith the polymerizable vinyl monomer.

(In formula (1), n represents 1 to 5, and when a equals 1, b equals 2,while when a equals 2, b equals 1).

(In formula (3), n represents 1 to 5).

(In formula (5), n represents 1 to 6).

Specific examples of the polymerizable phosphoric acid monomerrepresented by the above formula (1) include “KAYAMER® PM-21”manufactured by Nippon Kayaku Co., Ltd., which is a mixture of thefollowing at a molar ratio of 1:1: the compound represented by the aboveformula (1) where n=1, a=1 and b=2; and the compound represented by theabove formula (1) where n=1, a=2 and b=1. Specific examples of thepolymerizable phosphoric acid monomer represented by the above formula(2) include “KAYAMER® PM-2” manufactured by Nippon Kayaku Co., Ltd. and“LIGHT ESTER P-2M” manufactured by KYOEISHA CHEMICAL CO., LTD. Specificexamples of the polymerizable phosphoric acid monomer represented by theabove formula (3) include “KAYAMER® PM-1” (a compound represented by theabove formula (3) where n=1) manufactured by Nippon Kayaku Co., Ltd.,“LIGHT ESTER P-1M” (a compound represented by the above formula (3)where n=1) manufactured by KYOEISHA CHEMICAL CO., LTD, “Phosmer™ M” (acompound represented by the above formula (3) where n=1) manufactured byUni-Chemical Co., Ltd. and “Phosmer™ PE” (a compound represented by theabove formula (3) where n=4 to 5) manufactured by Uni-Chemical Co., Ltd.Specific examples of the polymerizable phosphoric acid monomerrepresented by the above formula (4) include “Phosmer™ CL” manufacturedby Uni-Chemical Co., Ltd. Specific examples of the polymerizablephosphoric acid monomer represented by the above formula (5) include“Phosmer™ PP” (a compound represented by the above formula (5) where n=5to 6) manufactured by Uni-Chemical Co., Ltd.

When the polymerizable phosphoric acid monomer is used together with thepolymerizable vinyl monomer in the present invention, the amount of thepolymerizable phosphoric acid monomer to be used preferably falls withinthe range from 0.01 to 1 part by weight with respect to 100 parts byweight of the polymerizable vinyl monomer, and further preferably,within the range from 0.01 to 0.8 part by weight. If the used amount ofthe polymerizable phosphoric acid monomer exceeds 1 part by weight withrespect to 100 parts by weight of polymerizable vinyl monomer used,composite particles such as emulsified particles (by-product fineparticles produced by emulsion polymerization) having an excessivelysmall particle diameter are likely to be produced when polymerizing,which may results in a problem of increase in the coefficient ofvariation in the size of the composite particles.

(Aqueous Medium)

In the polymerization step in the producing method of the presentinvention, examples of the aqueous medium for subjecting thepolymerizable monomer to the aqueous suspension polymerization includewater, and a mixed medium of water and an water-soluble medium (e.g.,alcohol such as methanol or ethanol). In order to stabilize thecomposite particles, it is preferable, generally, to use 100 to 1000parts by weight of aqueous medium with respect to 100 parts by weight ofthe polymerizable monomer used.

(Polymerization Initiator)

In the polymerization step in the producing method of the presentinvention, it is preferable to subject the polymerizable monomer to theaqueous suspension polymerization in the presence of a polymerizationinitiator.

As the polymerization initiator, an oil-soluble peroxide polymerizationinitiator or an oil-soluble azo polymerization initiator can be suitablyused, which are generally used for the aqueous suspensionpolymerization.

Examples of the peroxide polymerization initiator include benzoylperoxide, lauroyl peroxide, octanoyl peroxide, ortho-chlorobenzoylperoxide, ortho-methoxybenzoyl peroxide, methyl ethyl ketone peroxide,diisopropyl peroxydicarbonate, cumene hydroperoxide, cyclohexanoneperoxide, t-butylhydroperoxide and diisopropylbenzene hydroperoxide.

Examples of the azo polymerization initiator include2,2′-azobisisobutyronitrile, 2, 2′-azobis(2,4-dimethylvaleronitrile),2,2′-azobis(2,3-dimethylbutyronitrile),2,2′-azobis(2-methylbutyronitrile),2,2′-azobis(2,3,3-trimethylbutyronitrile),2,2′-azobis(2-isopropylbutyronitrile),1,1′-azobis(cyclohexane-1-carbonitrile),2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile),(2-carbamoylazo)isobutyronitrile, 4,4′-azobis(4-cyanovaleric acid) anddimethyl-2,2′-azobisisobutyrate.

Among the above polymerization initiators, it is preferable, from thestandpoint of decomposition rate and the like, to use2,2′-azobisisobutyronitrile, 2,2′-azobis(2,4-dimethylvaleronitrile),benzoyl peroxide, lauroyl peroxide and the like as the polymerizationinitiator for the producing method in the present invention.

The amount of the polymerization initiator to be used is preferably 0.01to 10 parts by weight with respect to 100 parts by weight of thepolymerizable monomer, and is further preferably 0.1 to 5.0 parts byweight. If the used amount of the polymerization initiator is less than0.01 part by weight with respect to 100 parts by weight of thepolymerizable monomer used, the polymerization initiator hardly servesits function sufficiently. If the used amount of the polymerizationinitiator is more than 10 parts by weight, it is difficult to obtaineffects corresponding to the used amount, which results in costdisadvantages.

(Silica Particles in State in which Water-Soluble Cellulose CompoundAdsorb onto Surfaces Thereof)

In the polymerization step in the producing method of the presentinvention, the polymerizable monomer is subjected to the aqueoussuspension polymerization in the presence of the silica particles andthe water-soluble cellulose compound adsorbing onto the surfaces of thesilica particles. In the polymerization step, the silica particles, ontothe surfaces of which adsorb the water-soluble cellulose compound, serveas a suspension stabilizer.

The silica particles are not particularly limited. Any known silicaparticles can be used. It is preferable to use the silica particleshaving the average primary particle diameter of 500 nm or less. If thesilica particles having the average primary particle diameter of morethan 500 nm are used, the amount to be added for stably performing thesuspension polymerization increases, which results in costdisadvantages. Moreover, it is unfavorable because of the difficulty instable dispersion of the polymerizable monomer. The average primaryparticle diameter of the silica particles is preferably as small aspossible. Specifically, it is preferably in the range from 5 to 150 nm,and further preferably, in the range from 8 to 100 nm.

As the silica particles, colloidal silica can be suitably used. Examplesof the colloidal silica include colloidal silica powder such asprecipitated silica powder and gas phase process silica powder, andcolloidal silica sol obtained by stably dispersing the silica particlesin a medium up to the primary particle level. Among them, the colloidalsilica sol obtained by stably dispersing the silica particles in themedium up to the primary particle level is more suitable for use in theproducing method in the present invention.

As the colloidal silica sol, aqueous silica sol, organosilica sol andthe like can be suitably used. In particular, since the polymerizablemonomer is subjected to the aqueous suspension polymerization (i.e., anaqueous medium is used for polymerizing the polymerizable monomer) inthe producing method of the present invention, it is most desirable touse the aqueous colloidal silica from the standpoint of dispersionstability of the colloidal silica sol. It is preferable to use thecolloidal silica sol with the silica concentration (solid componentconcentration) of 5 to 50 wt %, as it is sold commercially and is easilyavailable.

Examples of the commercial product of the colloidal silica includeSNOWTEX® series manufactured by NISSAN CHEMICAL INDUSTRIES LTD., inparticular, SNOWTEX® for general use, which are composed of sphericalparticles having the particle diameter of 5 to 100 nm (alkaline:“ST-XS”; “ST-30”; “ST-50”; “ST-30L”; and “ST-ZL”, acidic: “ST-OXS”;“ST-O”; “ST-O-40”; “ST-OL” and “ST-OZL35”), SNOWTEX® composed of largespherical particles having the particle diameter of 70 to 480 nm(alkaline: “ST-MP-2040”; and “ST-MP-4540M”), chain-like shaped SNOWTEX®composed of elongated particles having the particle diameter of 40 to100 nm (alkaline: “ST-UP”, acidic: “ST-OUP”), pearl-necklace-shapedSNOWTEX® composed of coupled spherical particles having the particlediameter of 10 to 25 nm (alkaline: “ST-PS-S”; and “ST-PS-M”, acidic:“ST-PS-SO” and “ST-PS-MO”).

The amount of the silica particles to be used (hereinafter referred toas “additive amount”) is preferably 0.022 to 0.15 g/m² per unit surfacearea of the composite particles obtained by the present producingmethod. If the additive amount of the silica particles is less than0.022 g/m², the silica particles may insufficiently adhere to thesurfaces of the polymer particles in the composite particles. If theadditive amount of the silica particles is more than 0.15 g/m², it isdifficult to obtain effects corresponding to the additive amount, whichresults in cost disadvantages.

The water-soluble cellulose compound that adsorb onto the silicaparticles are not particularly limited. Examples thereof includecompounds: alkyl celluloses such as methyl cellulose; hydroxyalkylcelluloses such as hydroxymethyl cellulose, hydroxyethyl cellulose, andhydroxypropyl cellulose; and hydroxyalkyl alkylcelluloses such ashydroxyethyl methylcellulose, and hydroxypropyl methylcellulose. Amongthe above compounds, it is preferable to use at least one of thehydroxyalkyl celluloses and hydroxyalkyl alkylcelluloses, specifically,at least one of hydroxypropyl cellulose (HPC) and hydroxypropylmethylcellulose (HPMC). Also, the above compounds may be used singularlyor as a combination of at least two of them.

It is generally known that hydroxypropyl cellulose (HPC) has the lowercritical solution temperature (LCST) of 45° C. Examples of thecommercial product include NISSO® HPC series (e.g., “SSL”, “SL”, “L”,“M” and “H”) manufactured by NIPPON SODA CO., LTD.

Examples of the commercial product of hydroxypropyl methylcellulose(HPMC) include Metolose® series manufactured by Shin-Etsu Chemical Co.,Ltd., in particular, Metolose® 60SH series having the cloud point of 60°C. (“605H-50”, “60SH-4000” and “605H-10000”), Metolose® 65SH serieshaving the cloud point of 65° C. (“655H-50”, “65-SH-400”, “65SH-1500”and “655H-4000”), and Metolose® 90SH series having the cloud point of90° C. (“905H-100”, “90SH-400”, “90SH-4000” and “90SH-15000”).

The adsorption amount of the water-soluble cellulose compound onto thesilica particles is not particularly limited. It may be suitably setaccording to the specific surface area of the silica particle used inthe present invention. Preferably, the adsorption amount is 0.05 to 0.5g per 1 g of the silica particles.

The adsorption amount of the water-soluble cellulose compound onto thesilica particles can be measured, for example, by a method described in“KOBUNSHI RONBUNSHU” (Japanese Journal of Polymer Science andTechnology), Vol. 40, No. 10, pp. 697-702 (October, 1983), issued by TheSociety of Polymer Science, Japan. Specifically, it can be measured by[Method for Measuring Adsorption Amount of Water-Soluble CelluloseCompound onto Silica Particles] described later in Examples.

The producing method of the present invention preferably includes,before the polymerization step, an adsorption step in which the silicaparticles are treated with the water-soluble cellulose compound so thatthe water-soluble cellulose compound is adsorbed onto the surfaces ofthe silica particles.

The method for treating the silica particles with the water-solublecellulose compound so that the water-soluble cellulose compound adsorbonto the surfaces of the silica particles is not particularly limited,thus the known methods can be applied. For example, the following methodis preferable: physically adsorbing the water-soluble cellulose compoundonto the surfaces of the silica particles by making the silica particlescoexist with the water-soluble cellulose compound in an aqueous medium(specifically, the method described in the document “Rheological andInterfacial Properties of Silicone Oil Emulsions Prepared by PolymerPre-adsorbed onto Silica Particles”, which appears in Colloids SurfacesA: Physicochem. Eng. Aspects, Vol. 328, pp. 114-122, 2008). Thewater-soluble cellulose compound that adsorb onto the silica particlesby this method are in a stable state and hardly desorb from the silicaparticles in the polymerization step.

It is possible to physically adsorb the water-soluble cellulose compoundphysically onto the surfaces of the silica particles more effectively bymaking the silica particles coexist with the water-soluble cellulosecompound under the temperature condition where the water-solublecellulose compound has the temperature of (T-15)° C. or more (where Trepresents the lower critical solution temperature (° C.) or the cloudpoint (° C.) of the water-soluble cellulose compound), furtherpreferably, the water-soluble cellulose compound has the temperature of(T-15)° C. or more and (T+20)° C. or less. The water-soluble cellulosecompound has, depending on its properties, either the lower criticalsolution temperature or the cloud point.

The water-soluble cellulose compound that have not adsorbed onto thesilica particles in the adsorption step may be removed by centrifugationand the like before the polymerization step, or may be removed bywashing, after the polymerization step, in the purification step ofpurifying the composite particles obtained in the polymerization step.

In the polymerization step in the producing method of the presentinvention, a suspension stabilizer other than the silica particles maybe further used unless it prevents the effect of enhanced suspensionstability of the silica particles onto which the water-soluble cellulosecompound adsorb.

(Surfactant)

In the polymerization step in the producing method of the presentinvention, the polymerizable monomer may be subjected to the aqueoussuspension polymerization in the presence of a surfactant in order tofurther improve the suspension stability. As the surfactant, any of thefollowing may be used: an anionic surfactant; a cationic surfactant; anampholytic surfactant; and a nonionic surfactant.

Examples of the anionic surfactant include: sodium oleate; fatty acidsoap such as castor oil potash soap; alkyl sulfate ester salt such assodium lauryl sulfate and ammonium lauryl sulfate; alkylbenzenesulfonatesalt such as sodium dodecylbenzenesulfonate; alkylnaphthalenesulfonatesalt; alkanesulfonate salt; dialkyl sulfosuccinate salt; alkyl phosphateester salt; naphthalenesulfonic acid formalin condensate;polyoxyethylene alkylphenyl ether sulfate ester salt; andpolyoxyethylene alkyl sulfate ester salt.

Examples of the nonionic surfactant include: polyoxyethylene alkylether, polyoxyethylene alkyl phenyl ether, polyoxyethylene fatty acidester, sorbitan fatty acid ester, polyoxy sorbitan fatty acid ester,polyoxyethylene alkyl amine, glycerin fatty acid ester, andoxyethylene-oxypropylene block polymer.

Examples of the cationic surfactant include: alkyl amine salt such aslaurylamine acetate, and stearylamine acetate; and quaternary ammoniumsalt such as lauryl trimethyl ammonium chloride.

Examples of the ampholytic surfactant include: lauryldimethylamineoxide; phosphate ester surfactant; and phosphite ester surfactant.

The above surfactants may be used singularly or as a combination of atleast two of them. The kind and the amount to be used of the surfactantare suitably selected and adjusted in consideration of the particlediameter of the composite particles to be obtained and the dispersionstability of the polymerizable monomer at the time of the aqueoussuspension polymerization.

(Polymerization Inhibitor)

In the polymerization step in the producing method of the presentinvention, the polymerizable monomer may be subjected to the aqueoussuspension polymerization in the presence of a water-solublepolymerization inhibitor in order to suppress generation of emulsifiedparticles in aqueous system.

Examples of the water-soluble polymerization inhibitor include:nitrites; sulfites; hydroquinones; ascorbic acids; water-solublevitamins B; citric acid; and polyphenols.

(Other Additives)

In the polymerization step in the producing method of the presentinvention, the polymerizable monomer may be subjected to the aqueoussuspension polymerization in the presence of other additives such as apigment, a dye, an antioxidant and an ultraviolet absorber, unless theyprevent the effects of the present invention.

Examples of the pigment includes: inorganic pigments such as white lead,red lead, chrome yellow, carbon black, ultramarine, zinc oxide, cobaltoxide, titanium dioxide, iron oxide, titan yellow, and titan black;yellow pigments such as Naples yellow, naphtol yellow S, Hanza yellow10G, benzidine yellow G, benzidine yellow GR, quinoline yellow lake,permanent yellow NCG, and tartrazine lake; orange pigments such asmolybdate orange, permanent orange RK, benzidine orange G, andindanthrene brilliant orange OK; red pigments such as permanent red 4R,lithol red, pyrazolone, red 4R, watching red calcium salt, lake red D,brilliant carmine 6B, eosin lake, rhodamine lake B, alizarin lake, andbrilliant carmine B; purple pigments such as fast violet B, methylviolet lake, and dioxane violet; blue pigments such as alkali blue lake,victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue,partial chloride phthalocyanine blue, fast sky blue, and indanthreneblue BC; green pigments such as pigment green B, malachite green lake,and final yellow green G; and organic pigments such as isoindolinonepigment, quinacridone pigment, perinone pigment, perylene pigment,insoluble azo pigment, soluble azo pigment, and lake pigment.

Examples of the dye include: nitroso dye, nitro dye, azo dye, stilbeneazo dye, diphenylmethane dye, triphenylmethane dye, xanthene dye,acridine dye, quinoline dye, methine dye, polymethine dye, thiazole dye,indamine dye, indophenol dye, azine dye, oxazine dye, thiazine dye, andsulphur dye.

Examples of the antioxidant include: phenol antioxidants such as2,6-di-t-butyl-4-methylphenol (BHT),n-octadecyl-3′-(3′,5′-di-t-butyl-4′-hydroxyphenyl)propionate,pentaerythrityl tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate],1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate,1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene,3,9-bis[2-{3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy}-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5,5]undecane;phosphorus antioxidants such as distearyl pentaerythritol diophosphite,tris(2,4-di-t-butylphenyl) phosphite, bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite, tetrakis(2,4-di-t-butylphenyl)4,4′-biphenylene diphosphonite, bis(2-t-butyl-4-methylphenyl)pentaerythritol diphosphite,2,4,8,10-tetra-t-butyl-6-[3-(3-methyl-4-hydroxy-5-t-butylphenyl)propxyldibenzo[d,f][1,3,2]dioxaphosphepin;and amine antioxidants such as phenyl-1-naphthylamine, octylateddiphenylamine, 4,4-bis(α,α-dimethylbenzyl)diphenylamine, andN,N′-di-2-naphthyl-p-phenylenediamine.

Examples of the ultraviolet absorber include benzophenone ultravioletabsorber, benzotriazole ultraviolet absorber (e.g., “ADK STAB® LA-31”manufactured by ADEKA CORPORATION), and hydroxyphenyl triazineultraviolet absorber.

(Suspension Polymerization Method)

In the polymerization step in the producing method of the presentinvention, the polymerizable monomer is subjected to the aqueoussuspension polymerization in the presence of the silica particles andthe water-soluble cellulose compound adsorbing onto the surfaces of thesilica particles. For example, in the polymerization step, a monomermixture is prepared by mixing, with the polymerizable monomer, thepolymerization initiator and/or the polymerization inhibitor and/orother additives, if needed, then the prepared monomer mixture isdispersed in an aqueous medium including the silica particles and thewater-soluble cellulose compound adsorbing onto the surfaces of thesilica particles (the aqueous medium may further include, if needed, thesurfactant and/or other suspension stabilizers), thus the aqueoussuspension polymerization is performed.

As the method for dispersing the monomer mixture in the aqueous medium,for example, the following can be suitably used: a method in which themonomer mixture is directly added to the aqueous medium and thendispersed as monomer droplets by stirring force of propeller blades andthe like; a method in which the monomer mixture is directly added to theaqueous medium and then dispersed in the aqueous medium using ahomomixer as a disperser that generates a high shear force by a rotorand a stator; a method in which the monomer mixture is directly added tothe aqueous medium and then dispersed in the aqueous medium using anultrasonic disperser; a method in which the monomer mixture is directlyadded to the aqueous medium and then dispersed as droplets in theaqueous medium by causing collisions between the droplets of the monomermixture or collisions of the droplets of the monomer mixture against aninner wall of a reaction container using a high-pressure disperser suchas Microfluidizer or Nanomizer; and a method in which the monomermixture is pressed into the aqueous medium through a MPG (micro porousglass) porous membrane. Among the above methods, the method using thehigh-pressure disperser such as the Microfluidizer or the Nanomizer orthe method in which the monomer mixture passes through the MPG (microporous glass) porous membrane can be suitably used as the method fordispersing the monomer mixture in the aqueous medium because theparticle diameter can be more uniform by those methods than by the othermethods.

Then, the aqueous medium in which the monomer mixture is dispersed(i.e., aqueous suspension) is heated so as to start the suspensionpolymerization. During the polymerization reaction, it is preferable tostir the aqueous suspension. The stirring may be performed to the extentof, for example, preventing the monomer mixture from surfacing asdroplets, or preventing the composite particles produced by thepolymerization from settling out.

In the suspension polymerization, the polymerization temperature ispreferably set in the range from 30 to 120° C., and further preferably,in the range from 40 to 80° C. The period of time for maintaining thepolymerization temperature is preferably in the range from 0.1 to 20hours.

After completion of the polymerization, the obtained composite particlesare separated as hydrous cake by the methods such as suction filtration,centrifugal dehydration, centrifugal separation and pressuredehydration. The hydrous cake is further washed by water and dried, asneeded, thus the desired composite particles can be obtained.

The size and the shape of the composite particles of the presentinvention are not particularly limited. However, by the above method forproducing the composite particles, it is possible to obtain thecomposite particles having the volume average particle diameter of 1 to100 μm.

The average particle diameter of the obtained composite particles can beadjusted by adjusting: the mixing condition of the monomer mixture andthe aqueous medium; the respective additive amounts of other suspensionstabilizers, surfactants and the like; the stirring condition of thestirrer; and the dispersion condition.

In the above method for producing the composite particles, thepolymerizable monomer is subjected to the aqueous suspensionpolymerization in the presence of the silica particles and thewater-soluble cellulose compound adsorbing onto the surfaces of thesilica particles, which allows the silica particles to strongly adhereto the surfaces of the polymer particles due to the function of thewater-soluble cellulose compound adsorbing onto the surfaces of thesilica particles. For this reason, it is possible to obtain thecomposite particles in which the silica particles hardly fall off thesurface of the polymer particles.

[Composite Particles]

In the above method for producing the composite particles, it ispossible to obtain the composite particles of the present invention inwhich the silica particles adhere to the surfaces of the polymerparticles (a polymer of the polymerizable monomer). That is, as shown inthe TEM (transmission electron microscope) images of FIGS. 1 and 2, itis possible to obtain the composite particle in which at least part ofthe polymer particle is covered by a layer of the silica particles (seethe black part of FIGS. 1 and 2).

Specifically, the composite particles of the present invention includethe polymer particles, the silica particles that adhere to the surfacesof the polymer particles and the water-soluble cellulose compound.

In the composite particles of the present invention, the silicaparticles may adhere to the surfaces of the polymer particles via thewater-soluble cellulose compound, or may adhere directly to the surfacesof the polymer particles. In other words, in the composite particles ofthe present invention, the water-soluble cellulose compound may adhereto both of the silica particles and the polymer particles, or may adhereto either the silica particles or the polymer particles.

In the composite particles of the present invention, the adhesion amountof the silica particles to the surfaces of the polymer particles is notparticularly limited. However, preferably it falls within the range from0.010 to 0.10 g/m² per unit surface area of the composite particles.When the adhesion amount of the silica particles to the surfaces of thepolymer particles is 0.010 to 0.10 g/m² per unit surface area of thecomposite particles, it is possible to sufficiently obtain thecharacteristics of the composite particles in which the silica particlesadhere to the polymer particles. The adhesion amount of the silicaparticles to the surface of the polymer particle (g/m²) in the compositeparticle can be obtained, for example, by [Calculation Method ofAdhesion Amount] described later in Examples.

In the above-described composite particles of the present invention, thesilica particles strongly adhere to the surfaces of the polymerparticles because of the water-soluble cellulose compound beingcontained, thus, the silica particles hardly fall off the surfaces ofthe polymer particles.

[External Preparation]

The composite particles of the present invention can be contained in anexternal preparation as an additive for improving the use feeling suchas lubricity when applying, or as an additive for obscuring skin defectssuch as pores, freckles and wrinkles by a light diffusion effect. Theexternal preparation of the present invention contains the compositeparticles of the present invention.

The amount of the composite particles contained in the externalpreparation of the present invention can be suitably set according tothe kind of the external preparation. However, the contained amount ispreferably in the range from 1 to 80 wt %, and further preferably, inthe range from 3 to 70 wt %. When the content of the composite particlesis less than 1 wt % with respect to the total amount of the externalpreparation, the specific effect due to the contained compositeparticles may not be seen. When the content of the composite particlesis more than 80 wt %, the remarkable effect corresponding to increase ofthe content may not be seen, thus it is unfavorable from the standpointof the producing costs.

The external preparation of the present invention can be used as, forexample, medicines for external use and cosmetics. The kind of themedicine for external use is not particularly limited, provided that itis applied to the skin. Specific examples thereof include cream,ointment and emulsion. Examples of the cosmetics include: cleaningcosmetics such as soap, body shampoo, cleansing cream, facial scrub, andtoothpaste; make-up cosmetics such as make-up powder, face powder (loosepowder, pressed powder and the like), foundation (powder foundation,liquid foundation, emulsion foundation and the like), lipstick, lipcream, cheek color, preparations for eyes and brows (eyeshadow,eyeliner, mascara and the like), and manicure; lotion such as pre-shavelotion, and body lotion; external preparations for body such as bodypowder, and baby powder; skin care preparations such as lotion, cream,and milk (cosmetic milk); antiperspirant (liquid antiperspirant, solidantiperspirant, cream antiperspirant and the like); facial masks; hairwashing preparations; hair dye, hair styling preparations, aromaticcosmetics; bath preparations; sunscreen preparations; suntanpreparations; and shaving cream.

The composite particles to be contained in the external preparation ofthe present invention may be treated with oil, a surface treatment agentsuch as a silicone compound and a fluorine compound, organic powder andinorganic powder.

As the oil, any oil that is generally used for the external preparationmay be used. Examples of the oil include: hydrocarbon oil such as liquidparaffin, squalane, vaseline, and paraffin wax; higher fattiy acid suchas lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid,behenic acid, undecylenic acid, oxystearic acid, linoleic acid, lanolinfatty acid, and synthetic fatty acid; estel oil such as glyceryltrioctanoate, propyleneglycol dicaprylate, cetyl 2-ethylhexanoate, andisocetyl stearate; waxes such as beeswax, whale wax, lanolin, carnaubawax, and candelilla wax; oils and fats such as linseed oil, cottonseedoil, castor oil, egg-yolk oil, and coconut oil; metal soaps such as zincstearate, and zinc laurate; higher alcohols such as cetyl alcohol,stearyl alcohol, and oleyl alcohol. The method for treating thecomposite particles with the oil is not particularly limited. Forexample, the following methods can be used: a dry method in which theoil is added to the composite particles and the mixture is stirred by amixer and the like so that the oil coats the composite particles; and awet method in which the oil is heated and dissolved in a suitablesolvent such as ethanol, propanol, ethyl acetate or hexane, thecomposite particles are added to the above solution and are stirred andmixed, then the solvent is removed under the reduced pressure or byheating, so that the oil coats the composite particles.

As the silicone compound, any silicone compound that is generally usedfor the external preparation may be used. Examples of the siliconecompound include: dimethylpolysiloxane, methylhydrogenpolysiloxane,methylphenylpolysiloxane, acrylic silicone graft polymner, organicsilicone resin, and partially crosslinked organopolysiloxane polymer.The method for treating the composite particles with the siliconecompound is not particularly limited. For example, the above dry methodand wet method can be used. Also, the baking treatment may beadditionally performed, if needed. In the case that the siliconecompound is reactive, a catalyst and the like may be appropriatelyadded.

As the fluorine compound, any fluorine compound that is generally usedfor the external preparation may be used. Examples of the fluorinecompound include ester containing perfluoroalkyl groups,perfluoroalkylsilane, perfluoropolyether, and polymer containingperfluoro groups. The method for treating the composite particles withthe fluorine compound also is not particularly limited. For example, theabove dry method and wet method can be used. Also, the baking treatmentmay be additionally performed, if needed. In the case that the fluorinecompound is reactive, a catalyst and the like may be appropriatelyadded.

Examples of the organic powder include: natural polymer compound such asgum arabic, gum tragacanth, guar gum, locust bean gum, karaya gum, irismoss, quince seed, gelatin, shellac, rosin, and casein; semisyntheticpolymer compound such as sodium carboxymethyl cellulose, hydroxyethylcellulose, methyl cellulose, ethyl cellulose, sodium alginate, gumester, nitro cellulose, hydroxypropyl cellulose, and crystallinecellulose; and resin particles such as polyvinyl alcohol, polyvinylpyrrolidone, sodium polyacrylate, carboxyvinyl polymer, polyvinyl methylether, polyamide resin, silicone oil, nylon particles, polymethylmethacrylate particles, crosslinked polystyrene particles, siliconeparticles, urethane particles, polyethylene particles, and fluororesinparticles. Examples of the inorganic powder include iron oxide,ultramarine, iron blue, chromium oxide, chromium hydroxide, carbonblack, manganese violet, titanium oxide, zinc oxide, talc, kaolin, mica,calcium carbonate, magnesium carbonate, aluminum silicate, bariumsilicate, calcium silicate, magnesium silicate, silica, zeolite, bariumsulfate, firing calcium sulfate (calcinated plaster), calcium phosphate,hydroxyapatite, and ceramic powder. These organic powder and inorganicpowder may be subjected to the surface treatment previously. As thesurface treatment, publicly known treatments as described above may beused.

Also, the external preparation of the present invention can contain,depending on its purpose, a main agent or an additive generally used,provided that it does not prevent the effects of the present invention.Examples of the main agent or the additive include water, lower alcohol(alcohol having a carbon number of not more than 5), fats and waxes,hydrocarbon, higher fatty acid, higher alcohol, sterol, fatty acidester, metal soap, moisturizer, surfactant, polymer compound, colormaterial, perfume, clay and minerals, preservative, germicide,anti-inflammatory agent, antioxidant, ultraviolet absorber, organic orinorganic composite particles, PH adjuster (triethanol amine and thelike), special additive, and active ingredient of medicine.

Specific examples of the fats and waxes include avocado oil, almond oil,olive oil, cocoa butter, beef tallow, sesame oil, wheat germ oil,safflower oil, shea butter, turtle oil, camellia oil, persic oil, castoroil, grape oil, macadamia nut oil, mink oil, egg-yolk oil, Japan wax,coconut oil, rose hip oil, hydrogenated oil, silicone oil, orange roughyoil, carnauba wax, candelilla wax, whale wax, jojoba oil, montan wax,beeswax, and lanolin.

Specific examples of the hydrocarbon include liquid paraffin, vaseline,paraffin, ceresine, micro crystalline wax, and squalane.

Specific examples of the higher fatty acid include fatty acid having acarbon number of not less than 11 such as lauric acid, myristic acid,palmitic acid, stearic acid, oleic acid, behenic acid, undecylenic acid,oxystearic acid, linoleic acid, lanolin fatty acid, and synthetic fattyacid.

Specific examples of the higher alcohol include alcohol having a carbonnumber of not less than 6 such as lauryl alcohol, cetyl alcohol,cetostearyl alcohol, stearyl alcohol, oleyl alcohol, behenyl alcohol,lanolin alcohol, hydrogenated lanolin alcohol, hexyldecanol,octyldecanol, isostearyl alcohol, jojoba alcohol, and decyltetradecanol.

Specific examples of the sterol include cholesterol, dihydrocholesterol,and phytocholesterol.

Specific examples of fatty acid ester include: linoleic acid ester suchas ethyl linolate; lanolin fatty acid ester such as lanolin fatty acidisopropyl; lauric acid ester such as hexyl laurate; myristic acid estersuch as isopropyl myristate, myristyl myristate, cetyl myristate,octyldecyl myristate, and octyldodecyl myristate; oleic acid ester suchas decyl oleate, and octyldodecyl oleate; dimethyl octane acid estersuch as hexyldecyl dimethyl octanoate; isooctane acid ester such ascetyl isooctanoate (cetyl 2-ethyl hexanoate); palmitic acid ester suchas decyl palmitate; cyclic alcohol fatty acid ester such as glycerintrimyristate, glycerin tri(caprylate or caprate), propylene glycoldioleate, glycerin triisostearate, glycerin triisooctanoate, cetyllactate, myristyl lactate, diisostearyl malate, cholesteryl isostearate,and cholesteryl 12-hydroxystearate.

Specific examples of the metal soap include zinc laurate, zincmyristate, magnesium myristate, zinc palmitate, zinc stearate, aluminiumstearate, calcium stearate, magnesium stearate, and zinc undecylenate.

Specific examples of the moisturizer include glycerin, propylene glycol,1,3-butylene glycol, polyethylene glycol, sodium dl-pyrrolidonecarboxylate, sodium lactate, sorbitol, sodium hyaluronate, polyglycerol,xylite, and maltitol.

Specific examples of the surfactant include: anionic surfactants such ashigher fatty acid soap, higher alcohol sulfuric acid ester, N-acylglutamine acid salt, and phosphoric acid ester salt; cationicsurfactants such as amino acid, and quaternaty ammonium salt; ampholyticsurfactants such as betaine type, amino acid type, imidazoline type andlecithin; and nonionic surfactants such as fatty acid monoglyceride,polyethylene glycol, propylene glycol fatty acid ester, sorbitan fattyacid ester (e.g., sorbitan isostearate), sucrose fatty acid ester,polyglycerol fatty acid ester, and ethylene oxide condensate.

Specific examples of the polymer compound include: natural polymercompound such as gum arabic, gum tragacanth, guar gum, locust bean gum,karaya gum, iris moss, quince seed, gelatin, shellac, rosin, and casein;semisynthetic polymer compound such as sodium carboxymethyl cellulose,hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, sodiumalginate, gum ester, nitro cellulose, hydroxypropyl cellulose, andcrystalline cellulose; and synthetic polymer compound such as resinparticles including polyvinyl alcohol, polyvinyl pyrrolidone, sodiumpolyacrylate, carboxyvinyl polymer, polyvinyl methyl ether, polyamideresin, silicone oil, nylon particles, poly(meth)acrylic acid esterparticles (e.g., polymethyl methacrylate particles), polystyreneparticles, silicone particles, urethane particles, and polyethyleneparticles. Note that in these application documents, the term“(meth)acrylic” means methacrylic or acrylic.

Specific examples of the color material include: inorganic pigments suchas iron oxide (e.g., red iron oxide, yellow iron oxide and black ironoxide), ultramarine, iron blue, chromium oxide, chromium hydroxide,carbon black, manganese violet, titanium oxide, zinc oxide, talc,kaolin, calcium carbonate, magnesium carbonate, mica, aluminum silicate,barium silicate, calcium silicate, magnesium silicate, silica, zeolite,barium sulfate, firing calcium sulfate (calcinated plaster), calciumphosphate, hydroxyapatite, and ceramic powder; and tar dyes such as azodye, nitro dye, nitroso dye, xanthene dye, quinoline dye,anthraquinoline dye, indigo dye, triphenylmethane dye, phthalocyaninedye, and pyrene dye.

The powder materials for the polymer compound or for the color materialmay be subjected to the surface treatment previously. As the surfacetreatment, publicly known treatments may be used. Examples of thetreatments include: an oil treatment using hydrocarbon oil, ester oil,lanolin or the like; a silicone treatment using dimethylpolysiloxane,methylhydrogenpolysiloxane, methylphenylpolysiloxane or the like; afluorine compound treatment using polymers and the like having estercontaining perfluoroalkyl groups, perfluoroalkylsilane,perfluoropolyether and perfluoroalkyl groups, a silane coupling agenttreatment using 3-methacryloxypropyl trimethoxysilane, 3-glycidoxypropyltrimethoxysilane or the like; a titanium coupling treatment usingisopropyl triisostearoyl titanate, isopropyltris (dioctylpyrophosphate)titanate or the like; a metal soap treatment; an amino acid treatmentusing acyl glutamic acid or the like; a lecithin treatment usinghydrogenated egg-yolk lecithin or the like; a collagen treatment; apolyethylene treatment; a moisturizing treatment; an inorganic compoundtreatment; and a mechanochemical treatment.

Specific examples of the clay and minerals include: components havingseveral functions such as extender pigment and adsorbent, i.e., talc,mica, sericite, titanium sericite (sericite coated with titanium oxide),moscovite, and VEEGUM® manufactured by R. T. Vanderbilt Company, Inc.

Specific examples of the perfume include anisaldehyde, benzyl acetateand geraniol. Specific examples of the preservative and germicideinclude methylparaben, ethylparaben, propylparaben, benzalkonium, andbenzethonium. Specific examples of the antioxidant includedibutylhydroxytoluene, butylhydroxyanisole, propyl gallate, andtocopherol. Specific examples of the anti-inflammatory agent includeε-aminocaproic acid, glycyrrhizic acid, dipotassium glycyrrhizinate,β-glycyrrhetic acid, lysozyme chloride, guaiazulene, and hydrocortisone.These may be used singularly, or as a combination of at least two ofthem. Specific examples of the ultraviolet absorber include: inorganicabsorbers such as titanium oxide fine particles, zinc oxide fineparticles, cerium oxide fine particles, iron oxide fine particles, andzirconium oxide fine particles; and organic absorbers based on such asbenzoic acid, para-aminobenzoic acid, anthranilic acid, salicylic acid,cinnamic acid, benzophenone, and dibenzoyl methane.

Specific examples of the special additive include hormones such asestradiol, estrone, ethinyl estradiol, cortisone, hydrocortisone, andpredonisone; vitamins such as vitamin A, vitamin B, vitamin C, andvitamin E; skin astringents such as citric acid, tartaric acid, lacticacid, aluminium chloride, aluminium sulfate, potassium sulfate,aluminium chlorohydroxy allantoinate, zinc para-phenolsulfonate, andzinc sulfate; hair growth promoting agents such as cantharis tincture,capsicum tincture, ginger tincture, swertia japonica extract, garlicextract, hinokitiol, carpronium chloride, pentadecanoic acid glyceride,vitamin E, estrogen, and photosensitive element; whitening agents suchas magnesium L-ascorbyl phosphate, and kojic acid.

The external preparation of the present invention has good lubricitybecause it contains the composite particles of the present invention.Also, when the external preparation contains an aqueous solvent, it ispossible to obtain a good dispersibility of the composite particles dueto hydrophilicity of the silica particles that adhere to the surfaces ofthe polymer particles.

[Coating Agent]

The composite particles of the present invention can be contained in thecoating agent as a coating film softening agent, a flatting agent forcoating material, a light diffusing agent and the like. The coatingagent of the present invention contains the composite particles of thepresent invention.

The coating agent contains, as needed, a binder resin. As the binderresin, it is possible to use a resin soluble in the organic solvent orthe water, or a emulsion-type waterborne resin dispersible in the water.Any known binder resins may be used. Examples of the binder resinsinclude: acrylic resins such as trade names: “Dianal® LR-102” and“Dianal® BR-106” both manufactured by MITSUBISHI RAYON CO., LTD., andtrade name: “Medium VM” manufactured by Dainichiseika Color & ChemicalsMfg. Co., Ltd.; an alkyd resin; a polyester resin; a polyurethane resin;a chlorinated polyolefin resin; an amorphous polyolefin resin; and asilicone resin. These binder resins may be suitably selected inconsideration of the adhesiveness of the coating agent to a basematerial to be coated, or in consideration of the usage environment.

The amount of the composite particles to be contained is suitablyadjusted in consideration of the thickness of the coating film formed bythe coating agent containing the binder resin, the average particlediameter of the composite particles, the coating method, the intendeduse and the like. Preferably, the amount is in the range from 1 to 300parts by weight with respect to 100 parts by weight of the binder resin,and further preferably, in the range from 5 to 100 parts by weight. Whenthe amount of the composite particles is less than 1 part by weight withrespect to 100 parts by weight of the binder resin, the flatting effectmay not be sufficiently obtained. When the amount of the compositeparticles is more than 300 parts by weight with respect to 100 parts byweight of the binder resin, the composite particles may not besufficiently dispersed because of the excess viscosity of the coatingagent, which results in the poor appearance of the surface of thecoating film, for example, microcracks or the roughness of the surfaceof the coating film coated with the coating agent.

The coating agent contains, as needed, a medium. As the medium, it ispreferable to use a solvent that can dissolve the binder resin or adispersion medium that can disperse the binder resin. As the dispersionmedium or the solvent, it is possible to use both an aqueous medium andan oily medium. Examples of the oily media include: hydrocarbon solventssuch as toluene, xylene, and cyclohexane; ketone solvents such as methylethyl ketone, and methyl isobutyl ketone; ester solvents such as ethylacetate, and butyl acetate; and ether solvents such as dioxane, ethyleneglycol diethyl ether, and ethylene glycol monobutyl ether. Examples ofthe aqueous media include water, and alcohols (for example,isopropanol). These media may be used singularly or as a combination ofat least two of them. The amount of the medium to be contained in thecoating agent is generally in the range from 20 to 60 wt % based on thetotal amount of the coating agent.

Furthermore, the coating agent may contain other additives such as acuring agent, a colorant (e.g., extender pigment, coloring pigment,metallic pigment, mica pigment powder, and dye), an antistatic agent, aleveling agent, a fluidity modifier, an ultraviolet absorber, and alight stabilizer.

The base material to be coated with the coating agent is notparticularly limited. It may be selected according to the intended use.

For example, for optical use, a glass base material, a transparent basematerial constituted by a transparent base resin or the like is used asa base material to be coated. It is possible to produce an optical filmsuch as a light diffusion film or an antiglare film by using atransparent base material as the base material to be coated, and bycoating the transparent base material with the coating agent notcontaining the colorant (i.e., coating agent for light diffusion) so asto form a transparent coating film. In this case, the compositeparticles serve as a light diffusing agent.

Also, when paper is used as the base material to be coated, it ispossible to produce matte paper by coating the paper with the coatingagent not containing the colorant (i.e. coating agent for paper) so asto form the transparent coating film.

The coating method with the coating agent is not particularly limited.Any known methods may be used. Examples of the coating methods include acomma direct method, a spin coating method, a spray coating method, aroll coating method, a dipping method, a knife coating method, a curtainflow method, and a laminating method. The coating agent may be dilutedwith a diluent as needed in order to adjust the viscosity. Examples ofthe diluents include: hydrocarbon solvents such as toluene, and xylene;ketone solvents such as methyl ethyl ketone, and methyl isobutyl ketone;ester solvents such as ethyl acetate, and butyl acetate; ether solventssuch as dioxane, and ethylene glycol diethyl ether; water; and alcoholsolvents. The above diluents may be used singularly or as a combinationof at least two of them. When producing the optical film, it ispreferable to use the coating method in which unevenness derived fromthe composite particles is formed on the surface of the coating film.

Since the above-described coating agent of the present inventioncontains the composite particles of the present invention, it ispossible to give the light diffusibility to the coating film formed bythe coating agent. Also, in the coating agent, the hardness of thecomposite particles is ensured by the silica particles that adhere tothe surfaces of the polymer particles. Thus, the improvement in thescratch resistance of the coating film formed by the coating agent canbe expected. Furthermore, when the coating agent contains the aqueoussolvent, it is possible to obtain an excellent dispersibility of thecomposite particles due to the hydrophilicity of the silica particlesthat adhere to the surfaces of the polymer particles.

[Optical Film]

The optical film of the present invention is obtainable by coating afilm-like base material with the coating agent of the present invention.Specific examples of the optical films include a light diffusion film,and an antiglare film.

Specific examples of the base material of the optical film include aglass base material, and a transparent base material made of atransparent base resin.

Examples of the transparent base resins include: an acrylic resin suchas polymethyl methacrylate; alkyl (meth)acrylate-styrene copolymer;polycarbonate; polyester such as polyethylene terephthalate (hereinafterreferred to as “PET”); polyethylene; polypropylene; and polystyrene.Among the above transparent base resins, when an excellent transparencyis required of the transparent base resin, it is preferable to use theacrylic resin, alkyl (meth)acrylate-styrene copolymer, polycarbonate,polyester or polystyrene. These transparent base resins may be usedsingularly or as a combination of at least two of them.

Also, in the optical film, the thickness of the coating film obtainableby applying the coating agent is preferably in the range from 5 to 100μm.

[Resin Composition]

The resin composition of the present invention contains the compositeparticles and the base resin of the present invention. Since the resincomposition of the present invention contains the composite particles ofthe present invention and is excellent in light diffusibility, it can beused as a material of a lighting cover (lighting cover for lightemitting diode (LED) lighting, lighting cover for fluorescent lightingand the like), and a material for light diffusers such as a lightdiffusion sheet and a light diffusion plate.

As the base resin, generally a thermoplastic resin is used, which isdifferent from the polymer components contained in the compositeparticles. Examples of the thermoplastic resins used as the base resininclude an acrylic resin, alkyl (meth)acrylate-styrene copolymer,polycarbonate, polyester, polyethylene, polypropylene, and polystyrene.Among these thermoplastic resins, when an excellent transparency isrequired of the base resin, it is preferable to use the acrylic resin,alkyl (meth)acrylate-styrene copolymer, polycarbonate, polyester orpolystyrene. These thermoplastic resins may be used singularly or as acombination of at least two of them.

The addition rate of the composite particles to the base resin ispreferably in the range from 0.1 to 70 parts by weight with respect to100 parts by weight of the base resin, and further preferably, in therange from 1 to 50 parts by weight. When the addition rate of thecomposite particles to the base resin is less than 0.1 part by weightwith respect to 100 parts by weight of the base resin, the lightdiffuser may not have the sufficient light diffusibility. When theaddition rate of the composite particles to the base resin is more than70 parts by weight with respect to 100 parts by weight of the baseresin, the optical transparency of the light diffuser may be reducedwhile the light diffuser obtains the light diffusibility.

The method for producing the resin composition is not particularlylimited. It can be produced by mixing the composite particles and thebase resin using a conventionally known method such as a mechanicalpulverizing and mixing method. In the mechanical pulverizing and mixingmethod, the resin composition can be produced by mixing and stirring thecomposite particles and the base resin using, for example, a mixer suchas a Henschel mixer, a V-type mixer, a Turbula mixer, a Hybridizer, or aRocking mixer.

[Molded Product]

The molded product of the present invention is obtainable by molding theresin composition of the present invention. Specific examples of themolded products of the present invention include a lighting cover(lighting cover for light emitting diode (LED) lighting, lighting coverfor fluorescent lighting and the like), and light diffusers such as alight diffusion sheet and a light diffusion plate.

For example, the composite particles and the base resin are mixed by themixer. The mixture is kneaded by a melt-kneader such as an extruder soas to obtain a pellet constituted by the resin composition. Then, thepellet is subjected to extrusion molding or it is melted and subjectedto injection molding. Thus, the molded product in a desired shape can beobtained.

EXAMPLES

Hereinafter, the present invention is described in detail with referenceto the Examples and the Comparative Examples. However, the presentinvention is not limited by the Examples. First, each measuring methodin the Examples and the Comparative Examples is described.

[Method for Measuring Average Primary Particle Diameter of SilicaParticles]

The average primary particle diameter (specifically, Z average particlediameter calculated by a cumulant analysis) of the silica particles ismeasured, for example, by a particle diameter measuring device usingdynamic light scattering method (“Zetasizer Nano ZS” manufactured byMalvern Instruments Ltd.).

As a measurement sample, a dispersion obtained by dispersing the silicaparticles to be measured in deionized water is used. When the assumedaverage primary particle diameter of the silica particles is less than100 nm, the dispersion is prepared so that the concentration of thesilica particles is 1 wt %. When the assumed average primary particlediameter of the silica particles is not less than 100 nm, the dispersionis prepared so that the concentration of the silica particles is 0.1 wt%. A polyethylene cell is set in a measurement unit of the particlediameter measuring device using dynamic light scattering method(“Zetasizer Nano ZS” manufactured by Malvern Instruments Ltd.) and thedispersion is dispensed on the polyethylene cell, so that the Z averageparticle diameter of the silica particles is measured.

The Z average particle diameter is a value obtained by analyzing, usingthe cumulant analysis, measurement data of the particle dispersion andthe like by the dynamic light scattering method.

By the cumulant analysis, an average value of the particle diameter anda polydispersity index (PDI) can be obtained. The average value of theparticle diameter is defined as the Z average particle diameter. Morestrictly, the cumulant analysis means fitting a polynomial to alogarithm of G1 correlation function obtained by the measurement. Theconstant b is called a secondary cumulant or a Z average diffusioncoefficient in the following formula:

LN(G1)=A+bt+ct ² +dt ³ +et ⁴+ . . . .

The Z average particle diameter is obtained by converting the aboveconstant b into the particle diameter using the viscosity of thedispersion and several device constants.

[Method for Measuring Adsorption Amount of Water-Soluble CelluloseCompound onto Silica Particles]

In Examples 1 to 3 described later, the dispersion medium containing thesilica particles onto which the water-soluble cellulose compound adsorbis used, which is obtained by the method for producing the compositeparticles. The adsorption amount (g) of the water-soluble cellulosecompound per 1 g of the silica particles is measured by the methoddescribed below.

The dispersion medium in an amount of 0.25 g, which contains the silicaparticles onto which the water-soluble cellulose compound adsorb, isdiluted with 1 g of deionized water. Then, the diluted dispersion mediumis centrifuged at 25000 G for 30 minutes using a centrifuge (“HitachHigh Speed Refrigerated Centrifuge HIMAC CR22GII”, manufactured byHitachi High-Technologies Corporation). To 1 ml of the obtainedsupernatant liquid, 1 ml of 5% phenol aqueous solution is added, andfurther 5 ml of concentrated sulfuric acid is added. The mixture is leftfor 10 minutes, and further is left still in the aqueous solution of 25°C. for 10 minutes, thus the measurement sample is obtained. Theabsorbance of the measurement sample at 485 nm is measured using anultraviolet and visible spectrophotometer (“Ultraviolet and VisibleSpectrophotometer UV-2450” manufactured by SHIMADZU CORPORATION). Thus,the concentration of the water-soluble cellulose compound (g/1) in thesupernatant liquid is obtained using a calibration curve (curveindicating the relation between the absorbance and the concentration ofthe water-soluble cellulose compound).

The calibration curve is made by the method described below. That is, 3kinds of aqueous solutions, each having a different concentration of thewater-soluble cellulose compound, are prepared, by adding to the 100 gof the deionized water respectively 0.01 g, 0.05 g and 0.1 g of thewater-soluble cellulose compound that are used for preparing thedispersion medium. Each of the prepared aqueous solutions in the amountof 0.25 g is diluted with 0.75 g of the deionized water. The absorbanceof each diluted aqueous solution is measured. Thus, the calibrationcurve, which is a primary curve, is made by plotting the weight of thewater-soluble cellulose compound in the aqueous solution and theabsorbance.

Then, the adsorption amount (g) of the water-soluble cellulose compoundper 1 g of the silica particles is obtained by the following formula:

D=(W _(H) −C×V)÷W _(S)

where D represents the adsorption amount (g) of the water-solublecellulose compound per 1 g of the silica particles, C represents theconcentration (g/1) of the water-soluble cellulose compound in thesupernatant liquid, W_(H) represents the weight (g) of the water-solublecellulose compound used for preparing the composite particles, W_(S)represents the weight (g) of the silica particles used for preparing thecomposite particles, and V represents the volume (1) of the aqueousmedium used for preparing the dispersion medium in the production of thecomposite particles.

[Method for Measuring Volume Average Particle Diameter]

The volume average particle diameter of the particles (compositeparticles or polymer particles) obtained in the Examples and ComparativeExamples described later is measured by Coulter Multisizer™ 3 (ameasurement device manufactured by Beckman Coulter, Inc.). Note that themeasurement is performed using the aperture calibrated according to theuser's manual of Multisizer™ 3 issued by Beckman Coulter, Inc.

Regarding the selection of the aperture used for the measurement, whenthe assumed volume average particle diameter of the particles to bemeasured (composite particles or polymer particles) is not less than 1μm and not more than 10 μm, the aperture having the size of 50 μm isselected. When the assumed volume average particle diameter of theparticles to be measured (composite particles or polymer particles) ismore than 10 μm and not more than 30 μm, the aperture having the size of100 μm is selected. When the assumed volume average particle diameter ofthe particles to be measured (composite particles or polymer particles)is more than 30 μm and not more than 90 μm, the aperture having the sizeof 280 μm is selected. When the assumed volume average particle diameterof the particles to be measured (composite particles or polymerparticles) is more than 90 μm and not more than 150 μm, the aperturehaving the size of 400 μm is selected. Thus, the size of the aperture isappropriately selected. When the measured volume average particlediameter is different from the assumed volume average particle diameter,a re-measurement is performed changing the aperture to the one having anappropriate size.

When the aperture having the size of 50 μm is selected, the “Current”(aperture current) is set to −800 and the “Gain” is set to 4. When theaperture having the size of 100 μm is selected, the “Current” (aperturecurrent) is set to −1600 and the “Gain” is set to 2. When the aperturesrespectively having the size of 280 μm and 400 μm are selected, the“Current” (aperture current) is set to −3200 and the “Gain” is set to 1.

As the measurement sample, the dispersion is used, which is obtained bydispersing 0.1 g of particles to be measured (composite particles orpolymer particles) in 10 ml of 0.1 wt % nonionic surfactant aqueoussolution using a touch mixer (“TOUCHMIXER MT-31” manufactured by YamatoScientific Co., Ltd.) and an ultrasonic cleaner (“ULTRASONIC CLEANERVS-150” manufactured by VELVO-CLEAR Co., Ltd.). A beaker filled withISOTON® II (electrolyte for measurement, manufactured by BeckmanCoulter, Inc.) is set in the measurement unit of the Coulter Multisizer™3. The dispersion is dripped while loosely stirring the inside of thebeaker. After an indication of the concentration meter, which is on thedisplay of the Coulter Multisizer™ 3 body, is set to 5 to 10%, themeasurement is started. During measurement, the content of the beaker isbeing loosely stirred to the extent that no air bubble enters. Themeasurement is terminated when a hundred thousand particles have beenmeasured. The volume average particle diameter of the particles(composite particles or polymer particles) is the arithmetic mean of thevolume particle size distribution of the hundred thousand particles.

[Method for Measuring Ignition Residue]

The particles to be measured (composite particles or polymer particles)are weighed to prepare 1.0 g thereof. The weighed particles are burnt inan electric furnace at 550° C. for 30 minutes. Then, the weight (g) ofthe residue is measured. The measured weight of the residue (g) isdivided by the weight of the particles before measurement (1.0 g), andthe obtained value is converted into percentage. Thus, the ignitionresidue (wt %) is obtained.

[Method for Measuring Specific Surface Area]

The particles to be measured (composite particles or polymer particles)are weighed to prepare 0.25 g thereof. The weighed particles are mixedwith 0.025 g of sodium dodecylbenzenesulfonate and 50 g of pure water.The mixture is stirred by ultrasonic for 10 minutes so as to dispersethe resin particles, thus the measurement sample is obtained. Thespecific surface area of the particles in the measurement sample ismeasured using a laser diffraction particle size analyzer (“Mastersizer2000” manufactured by Malvern Instruments Ltd.) under the measurementcondition specified below.

<Measurement Condition>

Dispersion medium: water

Analytic model: general purpose

Particle refractive index: 1.50

Dispersion medium refractive index: 1.33

[Method for Calculating Additive Amount of Silica Particles]

The additive amount (g/m²) of the silica particles per unit surface areaof the above-produced particles is obtained, using: the use weight ofthe silica particles and the use weight of the polymerizable vinylmonomer for producing the composite particles; and the specific surfacearea of the particles (composite particles or polymer particles)measured by the above-described measurement method of the specificsurface area, by the following calculation formula:

Additive amount=(W _(s) ÷W _(m))÷X

where W_(s) represents the use weight (g) of the silica particles forproducing the composite particles, W_(m) represents the use weight (g)of the polymerizable vinyl monomer for producing the compositeparticles, and X represents the specific surface area (m²/g) of theparticles measured by the above-described measurement method of thespecific surface area.

[Method for Calculating Adhesion Amount of Silica Particles]

In the particles obtained in the Examples and the Comparative Examplesdescribed later, the amount of the ignition residue is substantiallyequals the amount of the silica particles in the particles. Thus, theadhesion amount (g/m²) of the silica particles per unit surface area ofthe above-produced particles is obtained, using: the ignition residuemeasured by the above-described measurement method of the ignitionresidue; and the specific surface area of the particles measured by theabove-described measurement method of the specific surface area, by thefollowing calculation formula:

Adhesion amount=(A÷100)÷X

where A represents the ignition residue (wt %) measured by themeasurement method of the ignition residue, and X represents thespecific surface area (m²/g) of the particles measured by themeasurement method of the specific surface area.

In the above measurement method of the ignition residue, when theresidue that remains after burning the particles in the electric furnaceat 550° C. for 30 minutes contains components other than the silicaparticles, and thus when the amount of the ignition residue measured bythe measurement method of the ignition residue differs from the amountof the silica particles in the particles, the adhesion amount (g/m²) ofthe silica particles per unit surface area of the above-producedparticles can be obtained by the formula specified below. It is possibleto use the known methods such as the elemental analysis to determinewhether the residue contains the silica particles or not, or todetermine the amount of the silica particles contained in the residue.

Adhesion amount={(A÷100)×(B÷100)}÷X

where A represents the ignition residue (wt %) measured by themeasurement method of the ignition residue, B represents the contentrate (wt %) of the silica particles in the residue, and X represents thespecific surface area (m²/g) of the particles measured by themeasurement method of the specific surface area.

Example 1 Preparation Example of Composite Particles

Into a polymerization vessel having a mixer, the following were fed: 150g of water as the aqueous medium; 1.1 g of SNOWTEX® 0-40 (abbreviatedname: “ST-O-40”, which is colloidal silica produced by NISSAN CHEMICALINDUSTRIES LTD., with the average primary particle diameter of 25 nm and40 wt % solid content) (net amount of SiO₂: 0.44 g) as the silicaparticles; and 0.09 g of Metolose® 65SH-400 (abbreviated name: “HPMC(65SH-400)”, which is hydroxypropyl methylcellulose manufactured byShin-Etsu Chemical Co., Ltd., with the cloud point of 65° C.) as thewater-soluble cellulose compound, so that they were mixed at 60° C. for24 hours. Thus, the dispersion medium was obtained, which contained thesilica particles onto which the water-soluble cellulose compoundadsorbed. The adsorption amount of the water-soluble cellulose compoundonto the silica particles was measured using the dispersion medium,which resulted in 0.18 g of the water-soluble cellulose compoundadsorbing onto 1 g of the silica particles.

Separately, the monomer mixture containing the polymerization initiatorwas prepared by mixing uniformly and dissolving: 50 g of methylmethacrylate (MMA) and 2.5 g of ethylene glycol dimethacrylate (EDGMA)as the polymerizable vinyl monomer; and 0.5 g of2,2′-azobis(2,4-dimethylvaleronitrile) (ADVN) as the polymerizationinitiator.

The monomer mixture containing the polymerization initiator was added tothe dispersion medium in the polymerization vessel, and the mixture wasstirred at 4500 rpm for 3 minutes by a homomixer (High Flex DisperserHG-2, manufactured by SMT CO., LTD.), thus finely dispersing the monomermixture in the dispersion medium.

Then, stirring was continued at the stirring speed of 70 rpm. After thetemperature of the dispersion medium to which added the monomer mixturereached 55° C., the suspension polymerization was performed for 6 hours.

Then, the reaction liquid in the polymerization vessel was cooled to theroom temperature while being stirred. Subsequently, the reaction liquidwas subjected to suction filtration using qualitative filter paper 101(“TOYO Qualitative Filter Paper” manufactured by ADVANTEC, MFS, INC.),and was washed by deionized water and subjected to deliquoring, beforebeing dried in an oven at 90° C. for 24 hours. Thus, the compositeparticles were obtained.

The cross section of the obtained composite particles was confirmed bythe TEM (transmission electron microscope). As shown in FIGS. 1 and 2,it was confirmed that the composite particles contained the polymerparticles and the silica particles that adhered to the polymerparticles. It was also confirmed that a layer of the silica particleswas formed on the surface of the polymer particles in the compositeparticles.

Also, the obtained composite particles had the volume average particlediameter of 20.2 μm, the specific surface area of 0.29 m²/g, and theignition residue of 0.60 wt %. The additive amount of the silicaparticles was 0.029 g/m². The adhesion amount of the silica particles inthe obtained composite particles was 0.021 g/m² per unit surface area ofthe composite particles.

Example 2 Preparation Example of Composite Particles

The composite particles were obtained in the same way as Example 1except for using, as the water-soluble cellulose compound, 0.09 g ofMetolose® 65SH-4000 (abbreviated name: “HPMC (65SH-4000)”, which ishydroxypropyl methylcellulose manufactured by Shin-Etsu Chemical Co.,Ltd., with the cloud point of 65° C.), in place of 0.09 g of Metolose®65SH-400 (HPMC (655H-400)).

In the dispersion medium containing the silica particles onto which thewater-soluble cellulose compound adsorbed, which was obtained in thepreparation process of Example 2, the adsorption amount of thewater-soluble cellulose compound was 0.17 g onto 1 g of the silicaparticles. Also, the obtained composite particles had the volume averageparticle diameter of 24.6 μm, the specific surface area of 0.24 m²/g,and the ignition residue of 0.70 wt %. The additive amount of the silicaparticles was 0.035 g/m². The adhesion amount of the silica particles inthe obtained composite particles was 0.029 g/m².

Example 3 Preparation Example of Composite Particles

The composite particles were obtained in the same way as Example 1except for: using, as the water-soluble cellulose compound, 0.09 g ofMetolose® 65SH-50 (abbreviated name: “HPMC (65SH-50)”, which ishydroxypropyl methylcellulose manufactured by Shin-Etsu Chemical Co.,Ltd., with the cloud point of 65° C.), in place of 0.09 g of Metolose®65SH-400 (HPMC (65SH-400)); and further using 0.05 g of KAYAMER® PM-21(abbreviated name: “PM-21”, manufactured by Nippon Kayaku Co., Ltd.) asthe polymerizable phosphoric acid monomer in the preparation of themonomer mixture.

In the dispersion medium containing the silica particles onto which thewater-soluble cellulose compound adsorbed, which was obtained in thepreparation process of Example 3, the adsorption amount of thewater-soluble cellulose compound was 0.16 g onto 1 g of the silicaparticles. Also, the obtained composite particles had the volume averageparticle diameter of 21.8 μm, the specific surface area of 0.28 m²/g,and the ignition residue of 0.60 wt %. The additive amount of the silicaparticles was 0.030 g/m². The adhesion amount of the silica particles inthe obtained composite particles was 0.021 g/m².

Example 4 Preparation Example of Composite Particles

The composite particles were obtained in the same way as Example 1except for using, as the polymerizable vinyl monomer, 50 g of styrene(St) and 2.5 g of ethylene glycol dimethacrylate (EGDMA), in place of 50g of methyl methacrylate (MMA) and 2.5 g of ethylene glycoldimethacrylate (EDGMA).

The obtained composite particles had the volume average particlediameter of 20 μm, the specific surface area of 0.29 m²/g, and theignition residue of 0.80 wt %. The additive amount of the silicaparticles was 0.029 g/m². The adhesion amount of the silica particles inthe obtained composite particles was 0.028 g/m².

Example 5 Preparation Example of Composite Particles

The composite particles were obtained in the same way as Example 1except for using, as the silica particles, 2.3 g of SNOWTEX® OXS(abbreviated name: “ST-OXS”, which is colloidal silica manufactured byNISSAN CHEMICAL INDUSTRIES LTD., with the average primary particlediameter of 7.8 nm and 15 wt % solid content) (net amount of SiO₂: 0.35g), in place of 1.1 g of SNOWTEX® 0-40 (“ST-O-40”; net amount of SiO₂:0.44 g).

The obtained composite particles had the volume average particlediameter of 20.5 μm, the specific surface area of 0.29 m²/g, and theignition residue of 0.33 wt %. The additive amount of the silicaparticles was 0.023 g/m². The adhesion amount of the silica particles inthe obtained composite particles was 0.011 g/m².

Example 6 Preparation Example of Composite Particles

The composite particles were obtained in the same way as Example 1except for using, as the silica particles, 4.28 g of SNOWTEX® OZL-35(abbreviated name: “ST-OZL-35”, which is colloidal silica manufacturedby NISSAN CHEMICAL INDUSTRIES LTD., with the average primary particlediameter of 85 nm and 35 wt % solid content) (net amount of SiO₂: 1.5g), in place of 1.1 g of SNOWTEX® 0-40 (“ST-O-40”; net amount of SiO₂:0.44 g).

The obtained composite particles had the volume average particlediameter of 20.9 μm, the specific surface area of 0.29 m²/g, and theignition residue of 1.9 wt %. The additive amount of the silicaparticles was 0.10 g/m². The adhesion amount of the silica particles inthe obtained composite particles was 0.066 g/m².

Example 7 Preparation Example of Composite Particles

The composite particles were obtained in the same way as Example 1except for using, as the silica particles, 2.53 g of SNOWTEX® PS-MO(abbreviated name: “ST-PS-MO”, which is colloidal silica manufactured byNISSAN CHEMICAL INDUSTRIES LTD., spherical particles with the averageprimary particle diameter of 21.5 nm being coupled, with 15 wt % solidcontent) (net amount of SiO₂: 0.38 g), in place of 1.1 g of SNOWTEX®0-40 (“ST-O-40”; net amount of SiO₂: 0.44 g).

The obtained composite particles had the volume average particlediameter of 20.5 μm, the specific surface area of 0.29 m²/g, and theignition residue of 0.60 wt %. The additive amount of the silicaparticles was 0.025 g/m². The adhesion amount of the silica particles inthe obtained composite particles was 0.021 g/m².

Example 8 Preparation Example of Composite Particles

The composite particles were obtained in the same way as Example 3except for: using, as the water-soluble cellulose compound, 0.09 g ofNISSO HPC H (hydroxypropyl cellulose having the lower critical solutiontemperature of 45° C., manufactured by NIPPON SODA CO., LTD.) in placeof 0.09 g of Metolose® 65SH-50 (HPMC (65SH-50)); and further changingthe mixing temperature when preparing the dispersion medium from 60° C.to 40° C.

The obtained composite particles had the volume average particlediameter of 19.8 μm, the specific surface area of 0.29 m²/g, and theignition residue of 0.80 wt %. The additive amount of the silicaparticles was 0.029 g/m². The adhesion amount of the silica particles inthe obtained composite particles was 0.028 g/m².

Example 9 Preparation Example of Composite Particles

The composite particles were obtained in the same way as Example 1except for: changing the amount to be used of SNOWTEX® 0-40 (“ST-O-40”)as the silica particles to 2.75 g (net amount of SiO₂: 1.1 g); changingthe amount to be used of Metolose® 65SH-400 (HPMC (65SH-400)) as thewater-soluble cellulose compound to 0.22 g; and further changing therotational speed of the homomixer from 4500 rpm to 9000 rpm.

The obtained composite particles had the volume average particlediameter of 7.9 μm, the specific surface area of 0.63 m²/g, and theignition residue of 1.45 wt %. The additive amount of the silicaparticles was 0.033 g/m². The adhesion amount of the silica particles inthe obtained composite particles was 0.023 g/m².

Example 10 Preparation Example of Composite Particles

The composite particles were obtained in the same way as Example 1except for: changing the amount to be used of SNOWTEX® 0-40 (“ST-O-40”)as the silica particles to 0.55 g (net amount of SiO₂: 0.22 g); changingthe amount to be used of Metolose® 65SH-400 (HPMC (65SH-400)) as thewater-soluble cellulose compound to 0.04 g; and further changing therotational speed of the homomixer from 4500 rpm to 2500 rpm.

The obtained composite particles had the volume average particlediameter of 40.9 μm, the specific surface area of 0.13 m²/g, and theignition residue of 0.29 wt %. The additive amount of the silicaparticles was 0.033 g/m². The adhesion amount of the silica particles inthe obtained composite particles was 0.022 g/m².

Example 11 Preparation Example of Composite Particles

The composite particles were obtained in the same way as Example 1except for: changing the amount to be used of SNOWTEX® 0-40 (“ST-O-40”)as the silica particles to 0.28 g (net amount of SiO₂: 0.11 g); changingthe amount to be used of Metolose® 65SH-400 (HPMC (65SH-400)) as thewater-soluble cellulose compound to 0.02 g; and further changing therotational speed of the homomixer from 4500 rpm to 2500 rpm.

The obtained composite particles had the volume average particlediameter of 80.7 μm, the specific surface area of 0.06 m²/g, and theignition residue of 0.15 wt %. The additive amount of the silicaparticles was 0.033 g/m². The adhesion amount of the silica particles inthe obtained composite particles was 0.025 g/m².

Example 12 Preparation Example of Composite Particles

The composite particles were obtained in the same way as Example 1except for: changing the amount to be used of the water as the aqueousmedium to 200 g; changing the amount to be used of SNOWTEX® 0-40(“ST-O-40”) as the silica particles to 4.0 g (net amount of SiO₂: 1.6g); changing the amount to be used of Metolose® 65SH-400 (HPMC(65SH-400)) as the water-soluble cellulose compound to 0.32 g; using, asthe polymerizable vinyl monomer, 140 g of methyl methacrylate (MMA) and60 g of trimethylolpropane triacrylate (TMPTA) in place of 50 g ofmethyl methacrylate (MMA) and 2.5 g of ethylene glycol dimethacrylate(EDGMA); and using, as the polymerization initiator, 1.0 g of lauroylperoxide (LPO) in place of 0.5 g of2,2′-azobis(2,4-dimethylvaleronitrile) (ADVN).

The obtained composite particles had the volume average particlediameter of 20.1 μm, the specific surface area of 0.29 m²/g, and theignition residue of 0.70 wt %. The additive amount of the silicaparticles was 0.029 g/m². The adhesion amount of the silica particles inthe obtained composite particles was 0.024 g/m².

Comparative Example 1 Comparative Preparation Example of CompositeParticles

The suspension polymerization was attempted to be performed in the sameway as Example 1 except for not using Metolose® 65SH-400 (HPMC(65SH-400)) as the water-soluble cellulose compound. However, thecomposite particles were not obtained because of low stability of thedroplets of the monomer mixture in the dispersion medium.

Comparative Example 2 Comparative Preparation Example of CompositeParticles

The suspension polymerization was attempted to be performed in the sameway as Example 1 except for not using SNOWTEX® 0-40 (“ST-0-40”) as thesilica particles. However, the composite particles were not obtainedbecause of low stability of the droplets of the monomer mixture in thedispersion medium.

Comparative Example 3 Comparative Preparation Example of CompositeParticles

The suspension polymerization was attempted to be performed in the sameway as Example 1 except for using 0.09 g of Gohsenol™ GL-05 (abbreviatedname: “GL-05”, polyvinyl alcohol (PVA) manufactured by The NipponSynthetic Chemical Industry Co., Ltd.) in place of 0.09 g of Metolose®65SH-400 (HPMC (655H-400)) as the water-soluble cellulose compound inthe preparation of the dispersion medium. However, the compositeparticles were not obtained because of low stability of the droplets ofthe monomer mixture in the dispersion medium.

Comparative Example 4 Comparative Preparation Example of CompositeParticles

Into a polymerization vessel having a mixer, the following were fed: 200g of water as the aqueous medium; 2.67 g of SNOWTEX® OXS (abbreviatedname: “ST-OXS”, which is colloidal silica manufactured by NISSANCHEMICAL INDUSTRIES LTD., with the average primary particle diameter of7.8 nm and 1.5 wt % solid content) (net amount of SiO₂: 0.40 g) as thesilica particles; and 0.02 g of polyoxyethylene lauryl ether as thesurfactant, so that they were mixed at 30° C. for 1 hours. Thus, thedispersion medium was obtained, which contained the silica particles andthe surfactant.

Separately, the monomer mixture containing the polymerization initiatorwas prepared by mixing uniformly and dissolving: 140 g of methylmethacrylate (MMA) and 60 g of trimethylolpropane triacrylate (TMPTA) asthe polymerizable vinyl monomer; and 1.0 g of lauroyl peroxide (LPO) asthe polymerization initiator.

The monomer mixture containing the polymerization initiator was added tothe dispersion medium in the polymerization vessel, and the mixture wasstirred at 4500 rpm for 3 minutes by the homomixer to finely dispersethe monomer mixture in the dispersion medium, and then 1.0 g of PVA-420(polyvinyl alcohol (PVA) manufactured by KURARAY CO., LTD.) was added asa dispersion stabilizer.

Then, stirring was continued at the stirring speed of 100 rpm. After thetemperature of the dispersion medium to which added the monomer mixturereached 55° C., the suspension polymerization was performed for 6 hours.

Then, the reaction liquid in the polymerization vessel was cooled to theroom temperature while being stirred. Subsequently, the reaction liquidwas subjected to suction filtration using qualitative filter paper 101(“TOYO Qualitative Filter Paper” manufactured by ADVANTEC, MFS, INC.),and was washed by deionized water and subjected to deliquoring, beforebeing dried in an oven at 90° C. for 24 hours. Thus, the compositeparticles were obtained.

The obtained composite particles had the volume average particlediameter of 20.6 μm, the specific surface area of 0.29 m²/g, and theignition residue of 0.10 wt %. The additive amount of the silicaparticles was 0.0069 g/m². The adhesion amount of the silica particlesin the obtained composite particles was 0.0034 g/m².

Comparative Example 5 Comparative Preparation Example of CompositeParticles

The composite particles were attempted to be prepared in the same way asComparative Example 4 except for: using, as the silica particles, 1.0 gof SNOWTEX® OL (abbreviated name: “ST-OL”, which is colloidal silicamanufactured by NISSAN CHEMICAL INDUSTRIES LTD., with the averageprimary particle diameter of 70 nm and 20 wt % solid content) (netamount of SiO₂: 0.20 g), in place of 2.67 g of SNOWTEX® OXS (“ST-OXS”;net amount of SiO₂: 0.40 g); and changing the amount to be used of thepolyoxyethylene lauryl ether to 0.03 g. The particles obtained inComparative Example 5 had the volume average particle diameter of 20.4μm and the specific surface area of 0.29 m²/g. The additive amount ofthe silica particles was 0.0034 g/m², however, the ignition residue wasless than the quantitative lower limit. As the ignition residue was lessthan the quantitative lower limit, it was confirmed that the particlesobtained in Comparative Example 5 contained few silica particles. Thus,the particles were confirmed to be the polymer particles, not thecomposite particles.

Comparative Example 6 Comparative Preparation Example of CompositeParticles

The composite particles were attempted to be prepared in the same way asComparative Example 4 except for using, as the silica particles, 0.5 gof SNOWTEX® MP-2040 (abbreviated name: “ST-MP-2040”, which is colloidalsilica manufactured by NISSAN CHEMICAL INDUSTRIES LTD., with the averageprimary particle diameter of 200 nm and 40 wt % solid content) (netamount of SiO₂: 0.20 g), in place of 2.67 g of SNOWTEX® OXS (“ST-OXS”;net amount of SiO₂: 0.40 g). The particles obtained in ComparativeExample 6 had the volume average particle diameter of 20.1 μm and thespecific surface area of 0.29 m²/g. The additive amount of the silicaparticles was 0.0034 g/m², however, the ignition residue was less thanthe quantitative lower limit. As the ignition residue was less than thequantitative lower limit, it was confirmed that the particles obtainedin Comparative Example 6 contained few silica particles. Thus, theparticles were confirmed to be the polymer particles, not the compositeparticles.

Comparative Example 7 Comparative Preparation Example of CompositeParticles

The composite particles were attempted to be prepared in the same way asComparative Example 4 except for: using, as the silica particles, 1.5 gof SNOWTEX® MP-4540M (abbreviated name: “ST-MP-4540M”, which iscolloidal silica manufactured by NISSAN CHEMICAL INDUSTRIES LTD., withthe average primary particle diameter of 450 nm and 40 wt % solidcontent) (net amount of SiO₂: 0.60 g), in place of 2.67 g of SNOWTEX®OXS (“ST-OXS”; net amount of SiO₂: 0.40 g); and changing the amount tobe used of the polyoxyethylene lauryl ether to 0.06 g.

The particles obtained in Comparative Example 7 had the volume averageparticle diameter of 20.3 μm and the specific surface area of 0.29 m²/g.The additive amount of the silica particles was 0.010 g/m², however, theignition residue was less than the quantitative lower limit. As theignition residue was less than the quantitative lower limit, it wasconfirmed that the particles obtained in Comparative Example 7 containedfew silica particles. Thus, the particles were confirmed to be thepolymer particles, not the composite particles.

Comparative Example 8 Comparative Preparation Example of CompositeParticles

The composite particles were attempted to be prepared in the same way asExample 1 except for obtaining the dispersion medium containing thewater-soluble cellulose compound and the silica particles without mixingthe mixture at 60° C. for 24 hours (i.e., without the treatment toadsorb the water-soluble cellulose compound onto the silica particles)after feeding the water, the silica particles and the water-solublecellulose compound into the polymerization vessel having a mixer.However, the particles stuck to each other during the polymerization,thus the composite particles were not obtained.

Comparative Example 9 Comparative Preparation Example of CompositeParticles

The composite particles were attempted to be prepared in the same way asComparative Example 4 except for: changing the amount to be used ofSNOWTEX® OXS (“ST-OXS”) as the silica particles to 10.6 g (net amount ofSiO₂: 1.6 g); changing the amount to be used of the polyoxyethylenelauryl ether as the surfactant to 0.04 g; and further changing therotational speed of the homomixer from 4500 rpm to 9000 rpm.

The composite particles obtained in Comparative Example 9 had the volumeaverage particle diameter of 4.7 μm, the specific surface area of 1.06m²/g, and the ignition residue of 0.40 wt %. The additive amount of thesilica particles was 0.0075 g/m². The adhesion amount of the silicaparticles in the obtained composite particles was 0.0038 g/m².

Comparative Example 10 Comparative Preparation Example of CompositeParticles

The composite particles were attempted to be prepared in the same way asComparative Example 4 except for: changing the amount to be used ofSNOWTEX® OXS (“ST-OXS”) as the silica particles to 0.67 g (net amount ofSiO₂: 0.10 g); and changing the rotational speed of the homomixer from4500 rpm to 1500 rpm.

The particles obtained in Comparative Example 10 had the volume averageparticle diameter of 130 μm and the specific surface area of 0.04 m²/g.The additive amount of the silica particles was 0.010 g/m², however, theignition residue was less than the quantitative lower limit. As theignition residue was less than the quantitative lower limit, it wasconfirmed that the particles obtained in Comparative Example 10contained few silica particles. Thus, the particles were confirmed to bethe polymer particles, not the composite particles.

Regarding Examples 1 to 12 and Comparative Examples 1 to 10, Tables 1 to4 below indicate respectively the following: the respective amounts ofthe materials used for the production; the measurement results of therespective average primary particle diameters of the silica particlesused for the production; the measurement results of the respectivevolume average particle diameters, specific surface areas, and ignitionresidues of the particles (composite particles) obtained by theproduction; the calculation results of the respective additive amountsof the silica particles; and the calculation results of the respectiveadhesion amounts of the silica particles in the composite particlesobtained by the production.

TABLE 1 Examples 1 2 3 4 5 6 Used Materials (g) Polymerizable MMA 50 5050 — 50 50 Vinyl EGDMA 2.5 2.5 2.5 2.5 2.5 2.5 Monomers TMPTA — — — — —— St — — — 50 — — Polymerizable PM-21 — — 0.05 — — — Phosphoric AcidMonomers Polymerization ADVN 0.5 0.5 0.5 0.5 0.5 0.5 Initiator LPO — — —— — — Silica ST-O-40 1.1 1.1 1.1 1.1 — — Particles (0.44) (0.44) (0.44)(0.44) ST-OXS — — — — 2.3 — (0.35) ST-OZL-35 — — — — — 4.28 (1.5)ST-PS-MO — — — — — — ST-OL — — — — — — MP-2040 — — — — — — MP-4540M — —— — — — Water-Soluble NISSO HPC H — — — — — — Cellulose HPMC(65SH-50) —— 0.09 — — — Compound HPMC(65SH-400) 0.09 — — 0.09 0.09 0.09HPMC(65SH-4000) — 0.09 — — — — Sulfactant Polyoxyethylene Lauryl — — — —— — Ether PVA PVA-420 — — — — — — GL-05 — — — — — — Measurement/ SilicaAverage Primary 25 25 25 25 7.8 85 Calculation Results ParticlesParticle Diameter (nm) Composite Volume Average 20.2 24.6 21.8 20 20.520.9 Particles Particle Diameter (μm) Specific Surface Area 0.29 0.240.28 0.29 0.29 0.29 (m²/g) Ignition Residue 0.60 0.70 0.60 0.80 0.33 1.9(wt. %) Additive Amount 0.029 0.035 0.030 0.029 0.023 0.10 (g/m²)Adhesion Amount 0.021 0.029 0.021 0.028 0.011 0.066 (g/m²) Note 1: Thevalue in parentheses means net amount of SiO₂.

TABLE 2 Examples 7 8 9 10 11 12 Used Materials (g) Polymerizable MMA 5050 50 50 50 140 Vinyl EGDMA 2.5 2.5 2.5 2.5 2.5 — Monomers TMPTA — — — —— 60 St — — — — — — Polymerizable PM-21 — 0.05 — — — — Phosphoric AcidMonomers Polymerization ADVN 0.5 0.5 0.5 0.5 0.5 — Initiator LPO — — — —— 1.0 Silica ST-O-40 — 1.1 2.75 0.55 0.28 4.0 Particles (0.44) (1.1)(0.22) (0.11) (1.6) ST-OXS — — — — — — ST-OZL-35 — — — — — — ST-PS-MO2.53 — — — — — (0.38) ST-OL — — — — — — MP-2040 — — — — — — MP-4540M — —— — — — Water-Soluble NISSO HPC H — 0.09 — — — — Cellulose HPMC(65SH-50)— — — — — — Compound HPMC(65SH-400) 0.09 — 0.22 0.04 0.02 0.32HPMC(65SH-4000) — — — — — — Sulfactant Polyoxyethylene Lauryl — — — — —— Ether PVA PVA-420 — — — — — — GL-05 — — — — — — Measurement/ SilicaAverage Primary 21.5 25 25 25 25 25 Calculation Results ParticlesParticle Diameter (nm) Composite Volume Average 20.5 19.8 7.9 40.9 80.720.1 Particles Particle Diameter (μm) Specific Surface Area 0.29 0.290.63 0.13 0.06 0.29 (m²/g) Ignition Residue 0.60 0.80 1.45 0.29 0.150.70 (wt. %) Additive Amount 0.025 0.029 0.033 0.033 0.033 0.029 (g/m²)Adhesion Amount 0.021 0.028 0.023 0.022 0.025 0.024 (g/m²) Note 1: Thevalue in parentheses means net amount of SiO₂.

TABLE 3 Comparative Examples 1 2 3 4 5 Used Materials (g) PolymerizableMMA 50 50 50 140 140 Vinyl EGDMA 2.5 2.5 2.5 — — Monomers TMPTA — — — 6060 St — — — — — Polymerizable PM-21 — — — — — Phosphoric Acid MonomersPolymerization ADVN 0.5 0.5 0.5 — — Initiator LPO — — — 1.0 1.0 SilicaST-O-40 1.1 — 1.1 — — Particles (0.44) (0.44) ST-OXS — — — 2.67 — (0.40)ST-OZL-35 — — — — — ST-PS-MO — — — — — ST-OL — — — — 1.0 (0.20) MP-2040— — — — — MP-4540M — — — — — Water- NISSO HPC H — — — — — SolubleHPMC(65SH-50) — — — — — Cellulose HPMC(65SH-400) — 0.09 — — — CompoundHPMC(65SH-4000) — — — — — Sulfactant Polyoxyethylene Lauryl — — — 0.020.03 Ether PVA PVA-420 — — — 1.0 1.0 GL-05 — — 0.09 — — Measurement/Silica Average Primary 25 — 25 7.8 70 Calculation Results ParticlesParticle Diameter (nm) Composite Volume Average — — — 20.6 20.4Particles or Particle Diameter (μm) Polymer Specific Surface Area — — —0.29 0.29 Particles (m²/g) Ignition Residue — — — 0.10 * (wt. %)Additive Amount — — — 0.0069 0.0034 (g/m²) Adhesion Amount — — —0.0034 * (g/m²) Note 1: The value in parentheses means net amount ofSiO₂. Note 2: “*” means “less than quantitative lower limit”.

TABLE 4 Comparative Examples 6 7 8 9 10 Used Materials (g) PolymerizableMMA 140 140 50 140 140 Vinyl EGDMA — — 2.5 — — Monomers TMPTA 60 60 — 6060 St — — — — — Polymerizable PM-21 — — — — — Phosphoric Acid MonomersPolymerization ADVN — — 0.5 — — Initiator LPO 1.0 1.0 — 1.0 1.0 SilicaST-O-40 — — 1.1 — — Particles (0.44) ST-OXS — — — 10.6 0.67 (1.6) (0.10)ST-OZL-35 — — — — — ST-PS-MO — — — — — ST-OL — — — — — MP-2040 0.5 — — —— (0.20) MP-4540M — 1.5 — — — (0.60) Water-Soluble NISSO HPC H — — — — —Cellulose HPMC(65SH-50) — — — — — Compound HPMC(65SH-400) — — 0.09 — —HPMC(65SH-4000) — — — — — Sulfactant Polyoxyethylene Lauryl 0.02 0.06 —0.04 0.02 Ether PVA PVA-420 1.0 1.0 — 1.0 1.0 GL-05 — — — — —Measurement/ Silica Average Primary 200 450 25 7.8 7.8 CalculationResults Particles Particle Diameter (nm) Composite Volume Average 20.120.3 — 4.7 130 Particles or Particle Diameter (μm) Polymer SpecificSurface Area 0.29 0.29 — 1.06 0.04 Particles (m²/g) Ignition Residue * *— 0.40 * (wt. %) Additive Amount 0.0034 0.010 — 0.0075 0.010 (g/m²)Adhesion Amount * * — 0.0038 * (g/m²) Note 1: The value in parenthesesmeans net amount of SiO₂. Note 2: “*” means “less than quantitativelower limit”.

As can be seen the results shown in Tables 1 to 4, it was confirmed thatthe particles obtained in Examples 1 to 12 were the composite particlescontaining the polymer particles and the silica particles that adheredto the surfaces of the polymer particles. Also, in Examples 1 to 12,when the composite particles obtained by the suspension polymerizationwere subjected to washing and deliquoring, the silica particles hardlyfell off. Thus, it was confirmed that the composite particles obtainedin Examples 1 to 12 had the characteristics that the silica particlesstrongly adhere to the surfaces of the polymer particles, i.e., thesilica particles hardly fall off the surfaces of the polymer particles.Also, it was confirmed that, in the composite particles obtained inExamples 1 to 12, the adhesion amount of the silica particles to thesurfaces of the polymer particles was 0.010 to 0.10 g/m² (morespecifically, 0.011 to 0.066 g/m²), which was large. Thus, it wasconfirmed that, in the composite particles of the present invention,many silica particles adhere to the surfaces of the polymer particles.

In contrast, the particles were not obtained in Comparative Examples 1to 3 and 8. Also, in Comparative Examples 5 to 7 and 10, which wereaccording to the methods for producing the resin particle disclosed inPatent Literature 1, the polymer particles were obtained, however, theadhesion amount the silica particles to the surfaces of the polymerparticles was small relative to the additive amount (corresponding tothe “covered amount” of Patent Literature 1) of the silica particles.Specifically, in Comparative Examples 5 to 7 and 10, the additive amountof the silica particles was 0.0034 to 0.010 g/m², while the ignitionresidue was less than the quantitative lower limit. Thus, it was notconfirmed that the silica particles adhered to the surfaces of theobtained polymer particles. Also, in Comparative Examples 4 and 9, thecomposite particles containing the polymer particles and the silicaparticles that adhered to the surfaces of the polymer particles wereobtained. However, it was confirmed that when the composite particlesobtained by the suspension polymerization were subjected to washing anddeliquoring, the silica particles fell off. Thus, it was confirmed thatthe composite particles obtained in Comparative Examples 4 and 9 had thecharacteristics that the silica particles do not strongly adhere to thesurfaces of the polymer particles, i.e., the silica particles easilyfall off the surfaces of the polymer particles. Furthermore, inComparative Examples 4 and 9, the additive amount of the silicaparticles was 0.0069 to 0.0075 g/m², while the adhesion amount of thesilica particles to the surfaces of the polymer particles of theobtained composite particles was 0.0034 to 0.0038 g/m², which wassmaller than the above additive amount of the silica particles, and alsosmaller than the adhesion amount of the silica particles to the surfacesof the polymer particles of the composite particles in Examples 1 to 12.

Example 13 Preparation Example of Optical Film

A coating agent was obtained by mixing: 30 g of the particles (compositeparticles) obtained in Example 8; 100 g of acrylic polyol (trade name:“Mesium VM” manufactured by Dainichiseika Color & Chemicals Mfg. Co.,Ltd., with 34 wt % resin solid resin content, solvent dispersion type)as the binder resin; and 30 g of isocyanate (trade name: VM-D,manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.) as thecuring agent. After that, the obtained coating agent was applied, usingan applicator, onto a polyester film having the thickness of 100 μm as abase material. The coated film was subjected to hot-air drying at 70° C.for 10 minutes, thus, the optical film was obtained. Then, the totallight transmittance, the haze and the gloss of the obtained optical filmwere measured. The results are shown in Table 5 below.

TABLE 5 Total Light Transmittance Haze Gloss Example 13 95.7 88.7 12

[Method for Measuring Total Light Transmittance and Haze]

The haze and the total light transmittance of the optical film obtainedin Example 13 were measured by a haze meter “NDH-4000” manufactured byNIPPON DENSHOKU INDUSTRIES CO., LTD. The measurement of the total lighttransmittance was performed under JIS K 7361-1 test conditions, whilethe measurement of the haze was performed under JIS K 7136 testconditions. Note that the haze and the total light transmittance shownin Table 5 are each an average value of the measured values of twomeasurement samples (number of measurement samples n=2). The haze valueincreases as the diffusibility of the light that transmits the opticalfilm (transmitted light) increases.

[Method for Measuring Gloss]

The gloss of the optical film obtained in Example 13 was measured by agloss checker (gloss meter) “IG-331” manufactured by HORIBA, Ltd.Specifically, the gloss of the optical film at 60° was measured by thegloss checker (gloss meter) “IG-331” in accordance with the methoddescribed in JIS Z 8741. The gloss value decreases, which means that theflatting effect improves, as the diffusibility of the light reflectedfrom the surface of the optical film (more specifically, the surface ofthe coating film formed by applying the coating agent) increases.

Example 14 Method for Manufacturing External Preparation (Body Lotion)

Body lotion was obtained by sufficiently mixing, by a mixer, thefollowing: 3 parts by weight of the composite particles obtained inExample 8; 50 parts by weight of ethanol, 0.1 part by weight ofglycyrrhizic acid; 0.5 part by weight of perfume; and 46.4 parts byweight of purified water.

The present invention may be embodied in other forms without departingfrom the gist or essential characteristics thereof. The foregoingexamples are therefore to be considered in all respects as illustrativeand not limiting. The scope of the present invention is indicated by theappended claims rather than by the foregoing description, and allmodifications and changes that come within the meaning and range ofequivalency of the claims are intended to be embraced therein.

INDUSTRIAL APPLICABILITY

The composite particles of the present invention may be applicable, forexample, to: an additive (a flatting agent, a coating film softeningagent, a texturing agent or the like) to a coating agent (coatingcomposition) used as coating material, a paper coating agent, arecording paper coating agent or a coating agent for optical member suchas an optical film; a light diffusing agent added to a lightdiffusibility resin composition for producing a light diffuser (alighting cover, a light diffusion plate, a light diffusion film or thelike); an anti-blocking agent for a film such as a food wrap film; and amaterial for an external preparation including an additive for anexternal preparation (additive for improving lubricity, or forcorrecting skin defects such as freckles and wrinkles) such ascosmetics.

1. A method for producing composite particles containing polymerparticles and silica particles that adhere to the polymer particles,comprising a polymerization step of subjecting a polymerizable monomerto aqueous suspension polymerization in a presence of silica particlesand a water-soluble cellulose compound adsorbing onto surfaces of thesilica particles, so as to obtain the composite particles.
 2. The methodfor producing composite particles according to claim 1, wherein at leastone of hydroxypropyl cellulose and hydroxypropyl methylcellulose is usedas the water-soluble cellulose compound.
 3. The method for producingcomposite particles according to claim 1, further comprising, before thepolymerization step, an adsorption step of treating the silica particleswith the water-soluble cellulose compound so as to adsorb thewater-soluble cellulose compound onto the surfaces of the silicaparticles.
 4. The method for producing composite particles according toclaim 3, wherein, in the adsorption step, the water-soluble cellulosecompound is adsorbed onto the surfaces of the silica particles by makingthe silica particles coexist with the water-soluble cellulose compoundunder a temperature condition where the water-soluble cellulose compoundhas a temperature of (T-15)° C. or more (where T represents a lowercritical solution temperature (° C.) or a cloud point (° C.) of thewater-soluble cellulose compound).
 5. The method for producing compositeparticles according to claim 1, wherein an amount of the silicaparticles is from 0.022 to 0.15 g/m² per unit surface area of thecomposite particles.
 6. Composite particles obtainable by the method forproducing composite particles according to claim 1, wherein at leastpart of surfaces of the polymer particles is covered by a layer of thesilica particles.
 7. Composite particles comprising polymer particles,silica particles that adhere to surfaces of the polymer particles, andwater-soluble cellulose compound.
 8. The composite particles accordingto claim 7, wherein an adhesion amount of the silica particles to thesurfaces of the polymer particles is from 0.010 to 0.10 g/m² per unitsurface area of the composite particles.
 9. The composite particlesaccording to claim 7, wherein at least part of the surfaces of thepolymer particles is covered by a layer of the silica particles.
 10. Anexternal preparation comprising the composite particles according toclaim
 7. 11. A coating agent comprising the composite particlesaccording to claim
 7. 12. An optical film obtainable by applying thecoating agent according to claim 11 onto a base material.
 13. A resincomposition comprising: the composite particles according to claim 7;and a base resin.
 14. A molded product obtainable by molding the resincomposition according to claim 13.